The central region of the coenobium is generally hollow but, in some species, it is filled with water (V. globator) or gelatinous materials (V. aureus). You can help Wikipedia by expanding it. Your Mobile number and Email id will not be published. Scientists were fascinated with the evolution of Volvox colonies. These 4 cells again divide longitudinally to form 8 cells, of which 4 cells are central and 4 are peripheral. BMC Biol 9, 89 (2011). Nutrition is holophytic. A typical volvox colony consists of a hollow sphere of cells. In this case, the flagella of all the cells of the colony perform simultaneous action by which the entire colony rolls over the surface of the water. Volvox based on the comparative morphology and molecular phylogeny of chloroplast genes and the internal transcribed spacer (ITS) regions of nuclear rDNA using various strains originating from Japan and two preserved strains from the USA. Asexual reproduction takes place during summer under favorable conditions, which allow a rapid expansion of the volvox population. The female gametes are large and non-motile, produced singly within the oogonium. plakea stage). At the apical portion of the cell, two equal length whiplash types of flagella arise from the two basal granules, i.e. These flagella face the side of the surrounding water and beat to propel the whole colony through the water. If you have never observed Volvox under the microscope I would highly recommend seeking these microorganisms out because they are extremely interesting to observe in action. Last edited on 18 February 2022, at 16:03, http://www.pnf.org/compendium/Ferdinand_Julius_Cohn.pdf, "Light reaction in lower organisms. At this stage, the cells are arranged in the form of a hollow sphere with an opening towards the exterior side, called a phialopore (a small aperture). In V. rouseletti and V. minor, the protoplast of the zygote is converted into a single zoospore which by further divisions forms a new coenobium. Initially, the gonidium undergoes longitudinal division into the plane of the colony and forms 2 cells. In this case, the male colony produces lots of sperm packets while the female colony releases oogamete or ovum. Here, we performed a taxonomic study of monoecious species of Volvox sect. Through this end, antherozoid enters the oogonium. API Stress Coat vs Tap Water Conditioner: Which Is Better Choice! If you close your iris diaphragm more than you normally would at high magnification you will also be able to clearly see the flagella and the motion that enables them to move in a circular motion.if(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[250,250],'microscopeclarity_com-leader-1','ezslot_12',137,'0','0'])};__ez_fad_position('div-gpt-ad-microscopeclarity_com-leader-1-0'); Because of their spherical shape it can be difficult to get a clear picture of the entire cell unless you have some good flat field corrected objective lenses. Like in the asexual stage, the cells remain in a plate-like structure or are grouped into a hollow sphere and then undergo inversion in which the anterior side of the cells faces the outer side. Brandon is an enthusiast, hobbyist, and amateur in the world of microscopy. The zygote reserves enough food materials with other inclusions. The plakea of antherozoids dissociates and liberates the antherozoids. The divisions of the gonidial protoplast occurring in the formation of a daughter colony are always longitudinal and all cells of each cell generation divide at the same time. Volvox is widely studied to understand the process of morphogenesis. Below is the microscopic view of a colony of volvox: Volvox is a coenobial green-algae, {(the colony-plant body does not have a fixed number of cells e.g. Reproductive cells differ from vegetative cells. The posterior half of the coenobium forms some specialized enlarged cells or gametangia which may be either the female sex organs (oogonia) or the male sex organ (antheridia). Save my name, email, and website in this browser for the next time I comment. In the anterior portion, the cells of the colony remain only vegetative and comparatively smaller. They act as excretory organs. Volvox is a free-floating freshwater planktonic green alga of the class Chlorophyceae. [In this image] Volvoxes grow rapidly during warm seasons.You may find Volvox colonies of different sizes which represent different stages of the life cycle.Photo source: wiki. In the case of Volvox rouseletti and Volvox minor, the zygote`s protoplasm is changed into a single zoospore and it divides again to form a new coenobium. A sex-inducing pheromone is also capable of triggering an asexual or sexual reproduction. [Video] Volvox aureus under the microscope. Individually or sometimes in groups, the antherozoids are liberated from the antheridium by rupturing the antheridial wall. [In this figure]Left: The simple microscope used by Antony Van Leeuwenhoek to discover the microscopic organisms. Thousands of cells together form colonies. In V. globator, one half of the spherical sheet of cells shrinks in radius and invaginates, initiating inversion (Fig. At the beginning of the growing season (favorable conditions), the reproduction is asexual. The protoplasmic strands may be thin and delicate in V. aureus, round in V. globator, wedge-shaped in V. mononae, or may be absent as in V. tertius. Each cell performs all the metabolic functions independently such as respiration, photosynthesis, excretion, etc. Thus, a mass of small, naked, biflagellate, fusiform antherozoids 16 to 512 in number in an antheridium is formed. While every effort has been made to follow citation style rules, there may be some discrepancies. Since Volvox are algae that prefer to live in mineral-rich habitats, they occasionally grow so rapidly and abundantly along with other algae that they cause harm. Biflagellate antherozoids get attracted towards oogonium by the chemotactic movement and forms diploid zygote after fertilization. This means that Volvox are capable of converting sunlight into energy as primary producers. In monoecious species, antheridia develop first and the fertilization occurs between the antherozoid and ovum of other plants. [In this image] A close view of vegetative cells on the surface of a Volvox colony. Run out your favorite pond or lake and snag a sample today! green algae (volvox globator), wood engraving, published in 1894 - volvox stock illustrations. nagariensis and V. globator. Each individual cell possesses a red eyespot on its surface. This stage is called the plakea stage, or the cruciate plate stage. Its growth is frequently observed in temporary or permanent freshwater ponds, pools, ditches, and also in lakes. Volvox, genus of some 20 species of freshwater green algae (division Chlorophyta) found worldwide. Volvoxes can reproduce both asexually and sexually. The spring and rainy seasons are the usual periods of volvoxs active vegetative growth. Other species (e.g., V. rouseletii) are heterothallic or dioecious, as antheridia and oogonia develop in separate colonies. A single eyespot is present at the anterior end. The outer wall and exospore may be smooth, (V. globator) or spiny (V. speematospaera). Binomial nomenclature is a system used to denote living organisms by species by first indicating the genus and then the specific epithet. Volvox colony appears in the rainy season. Trip.com Volvox Globator - KnihkupectvVolvox Globator - Knihkupectv Trip.com Volvox Globator - Knihkupectv! Its difficult to comprehend how such a small organism can have such a large impact on the world that we live in. They are eukaryotic. Thus, they may fill the hollow middle region of the parent colony. Volvox aureus) (coenobium-plant body has a fixed number of cells, e.g., Pandorina moruma, number of cells are 4, 8, 16 or 32. Dutch microscopist, Antonie van Leeuwenhoek, first reported the Volvox colonies in 1700. Each of the daughter cells, thus formed, again divides length-wise so that an eight-cell plate is formed. Description. One of the most-common species, V. aureus, can form harmful algal blooms in warm waters with a high nitrogen content. Each coenobium also contains a smaller number of cells which perform asexual reproduction for the next several generations. The sex organs (gametangia) are produced fewer in number. The second division is also longitudinal and at a right angle to the first. The protoplast of an antheridium undergoes repeated cell divisions in a way similar to that observed in the development of an asexual gonidial cell into a daughter colony (i.e. By asexual reproduction, reproductive cells grow into daughter colonies within the parent colony. Within the genus Volvox, two main modes of embryo inversion have been recently established during the asexual developmental cycleinversion of type A and inversion of type Brepresented by the two species most thoroughly studied, respectively, Volvox carterif. Structure of Volvox: Volvox thallus is a motile colony with definite shape and number of cells. After maturing, the daughter colony comes out from the parent colony. Anterior cells of the particular colony of. They are just visible to the naked eyes, about 0.5 mm. Humans breathe oxygen, while plants breathe carbon dioxide. The coenobium is composed of a large number of biflagellate, pear-shaped cells. Their number varies from two to fifty in a single coenobium. The colonial behavior of the individual cells is thought to be how unicellular organisms transitioned into multicellular organisms. Common species are Volvox aureus, Volvox globator, V. carteri, V. barberi, etc. The number of cells per coenobium varies e.g. It occurs in small glacial pools containing Riccia and duckweed. They tend to thrive in areas that receive a large amount of rainwater. After fertilization (plasmogamy and karyogamy), a diploid zygote or oospore is formed. if(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[300,250],'microscopeclarity_com-medrectangle-4','ezslot_4',141,'0','0'])};__ez_fad_position('div-gpt-ad-microscopeclarity_com-medrectangle-4-0');Volvox do not eat in a traditional sense. Asexual reproduction occurs at the beginning of the growing season during favorable conditions. [In this image] The formation of gonidia at the inner side of Volvox. The antherozoids secrete a proteolytic enzyme. Antheridium also possesses an enlarged structure similar to gonidia. Diploid zygote nucleus divides meiotically into four haploid nuclei; of these, 3 degenerates and the remaining one nucleus survive with cytoplasmic contents escapes from the vesicle. Eudorina unicocca, number of cells 16, 32 or 64)}. Each antherozoid is a biflagellate, elongated, conical, or fusiform structure with a single nucleus and a small yellow-green or pale green chloroplast. The male gametes are spindle-shaped, narrow with a pair of apical cilia, and are produced in bunches within the antheridium. There is not much known about the origins of Volvox. Each gonidium divides repeatedly and produces a spherical group of daughter cells. The sperm then fertilizes the eggs, and the eggs are released back into the water until they hatch and mature. Dutch microscopist Antonie van Leeuwenhoek first reported the Volox colonies in 1700. The daughter colonies inside the parental one are ready to release. Egg cells lack flagella and remain attached to neighboring cells by the protoplasmic bridges. The zygote contains enough reserve food material and other inclusions. These are just four of the 20 species of Volvox currently classified. Volvox thallus is a motile colony with definite shape and number of cells. The cell wall is thin and firm in nature composed of cellulose. Volvox can be found in ponds, puddles, and bodies of still fresh water throughout the world. During the early spring Volvox globator Linn., and no other species, occurs in great abundance in the same pools that later con- tain Volvox aureus. There are 1 or 2 pyrenoids associated with the chloroplast. The four haploid cells migrate with the vesicle. Leeuwenhoek also discovered many other microscopic organisms, such as rotifers and paramecia, by using his simple microscopes. Nostoc Commune | Nostoc Characteristics & Life Cycle 2023, Cyanophyceae | Chroococcus Characteristics, Structure And Reproduction 2023, Blue Green Algae: Cyanobacteria | Division Cyanophyta (Guide 2023), What Is Algae | The Life Cycle Of Algae (Guide 2023), Spirogyra | Pond Scum: Life Of Freshwater Algae 2023, Oscillatoria | The Blue Green Algae (Guide 2023). They further undergo multiple mitotic cell division to form a colony and the life cycle continues. If you pick up a handful of pond scum and squeeze out the water, youll likely see the Volvox swimming upwards towards the light. However, taxonomic studies of species in Volvox sect. It is found in freshwater as green balls of a pinhead size. Each cell, finally, acquires a pair of flagella and a cell membrane. It possesses a large amount of reserve food and many pyrenoids. It is a plant-like protist. The colour of the pond looks greenish due to the rapid growth of volvox. Leeuwenhoek was the first scientist to observe them in 1700. After maturing, the daughter colony comes out from the parent colony. Each of these 8 cells divided by longitudinal division forms a 16-celled stage. The spherical colonies can contain up to 45,000 cells . document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); You can call me Aron and by profession, I am an academic educator in plant sciences. With the help of inversion, the anterior end of the cells changes its position from inner to outer, and the position of the phialopore becomes reversed, i.e., it changes its position from outer to inner. Corrections? These 8 cells are arranged in such a manner that their concave inner surface face toward the outer side of the colony to form a curved plate-like structure. During germination outer two wall layers becomes gelatinous and the inner layer forms a vesicle which later on gets filled with the zygote protoplast. Hey, buds I am HarunYou can call me Aron mostly my close friends call me by my pen name. The cup-shaped or curved plate-like chloroplast contains photosynthetic pigments (chlorophyll a, chlorophyll b, carotenoids, and xanthophylls) characteristic of green algae. The daughter colonies are originally formed inside-out, with their flagella pointing inwards. The movement of the colony is brought about by the joint action of the flagella of individual cells. The total number of cells in the colony varies from about 500 (Volox aureus) to about 2000 or more (Volvox globate). That is why the zygote has to undergo reduction division during the formation of a new colony. The coenobium is a hollow sphere of mucilaginous substance. So, in a nutshell, you and I are gonna have a chit-chat about plants, their life, and how these fascinating creatures help us. anterior-posterior plane of the coenobium. At the same time, the phialopore becomes enlarged, through which the lower part comes out and the edges of the phialopore hang backward. It is found in freshwater as green balls of a pinhead size. 1). There are an estimated one trillion species of microbes on earth with over 99.99% of the species yet to be discovered. Volvox globator is the most common species of Volvox. Volvox globator L. NCBI BLAST name: green algae Rank: species Genetic code: Translation table 1 (Standard) Mitochondrial genetic code: Translation table 1 (Standard) The number of cells constituting the multicellular individual in the volvocine species is a multiple of two, ranging from four (Tetrabaena) to 128 in non-Volvox species and more than 500 in Volvox.Each cell of most volvocine multicellular individuals has essentially the same cellular organization as that in C. reinhardtii (Vol. A large volvox colony could be as big as a pinhead size. So, they need to undergo a process of inversion. The stress may cause damage to the Volvoxs DNA. Kingdoms are the most basic classification of living things. Rashid's experience in fluorescence microscopy and computational image analysis helped him carry out the proposed microscopical analysis of embryonic development in the green micro-algae Volvox and other members of the family Volvocaceae. Because of their photosynthetic tendencies, the Volvox is rarely observed living in heavily shaded areas. The male colonies release sperm into the surrounding water while the female colonies have specialized cells that enlarge and become eggs. Volvox is a common freshwater free-floating chlorophytic green alga that belongs to Volvocaceae family under order Volvocales of division Chlorophyta. Each gonidium lies within a globular gelatinous sheath. Besides these, the eyespot controls the movement of the flagella as they are photoreceptive organs. The genus can be found within freshwater habitats such as ponds, puddles, ditches, and more. At this stage, the cells continue to divide longitudinally until the number of cells reaches the number specified for a particular species. Such coenobium consists of a smaller number of cells that reproduces asexually for the next six or more generations, every time increasing the number in the succeeding generations. Volvox Globator @ 30x. It grows as plankton on the surface of water bodies like temporary and permanent freshwater tanks, ponds, pools, and lakes. The oosphere possesses a parietal chloroplast, pyrenoids, and a centrally placed large nucleus. Whereas sexual reproduction takes place under unfavorable conditions towards the end of the summer months. Different Volvox species have different tactics to turn their embryos inside out (fig. In a coenobium, the cells destined to form sex organs are present in the posterior half. Volvox is a genus of green algae and they form colonies having thousands of cells. Dioecious colonies have a sex assigned to them, whether male or female. [2] It is colonial flagellate found in freshwaters. The gonidia, on the other hand, are not mobile. At the base of the flagella, 2-3 contractile vacuoles are present. For example, the change in Volvox cell shape during inversion happens in a process analogous to animal gastrulation (an embryo forming its gut). The cells in a coenobium are interconnected by protoplasmic strands and are arranged in a single layer towards the periphery. The daughter colony (coenobium) is still retained within the parent cell wall which eventually develops into a mucilaginous membrane surrounding it. Because of the plant-like activities, Volvoxes and all other green algae are autotrophic organisms.Volvoxes are an important part of the aquatic ecosystem. A volvox ball or colony is usually a cluster of 500-50,000 cells. globator, form a small but robust monophyletic group that is referred to as the sectionVolvox [58,62,64,67,68]. On the other hand, Volvox are capable of forming algal blooms which can harm the ecosystem. Volvox, like other green algae, is photosynthetic and it swims toward the light (called phototaxis) to keep itself illuminated. Volvox can reproduce asexually or sexually. Prior to the division, the gonidia are slightly pushed into the interior of the colony and can be distinguished as a row of vegetative cells by their larger size, rounded shape, absence of flagella and eyespot, prominent nucleus, several pyrenoids, and densely granular cytoplasm. An algal bloom is more frequent in warm waters having a high nitrogen content. These greatly enlarged cells are specialized asexual cells called gonidia (singular gonidium). After this, the cells develop flagella and the daughter colony escapes by moving through a pore-like opening at the free face of the sac. The protoplast is of different shapes depending upon the species. In the cytoplasm, each cell contains a cup-shaped chloroplast with one or more pyrenoids, an eyespot, 26 contractile vacuoles, and a single nucleus. Volvox convert sunlight into usable energy mainly through oxygenic photosynthesis. It contains two contractile vacuoles, a nucleus, a cup-shaped chloroplast with pyrenoids, and an eyespot. [In this figure] Volvox is a hollow sphere of 500 50,000 cells, called a colony or coenobium. When a sperm cell fertilizes an egg cell, a thick-walled hypnozygote is formed. The Volvox colonies are asexual which produce daughter colonies within the parent colony. The two flagella are equal, whiplash-type, and are attached to the anterior end. Thus, the zygote is retained by the coenobium which can be liberated by the disintegration of the gelatinous matrix. All Volvox species within the section Volvox exhibit type B inversion (see Additional File 1). The alga due to a specific swimming pattern is often referred to as, rolling alga. The male gametangia are called antheridia or androgonidia, and the female gametangia are called oogonia or gynogonidia. Fertilized cells form hypnozygotes that can survive during the winter or dry season. Sexual reproduction is of the oogamous type, and the coenobia may be homothallic (e.g., V. globator) or heterothallic (e.g., V. aureus). The protoplasm of the cell is embedded within a plasma membrane. It swims freely and divides and re-divides to form a new coenobium. There are around 20 species come under this genus. Oogonium is a unicellular, enlarged, semi flask-shaped cell, with a gelatinous sheath-like wall. Volvox is classified in the class Chlorophyceae due to the presence of chlorophyll.Scientific classificationDomain: EukaryotaKingdom: PlantaePhylum: ChlorophytaClass: ChlorophyceaeOrder: ChlamydomonadalesFamily: VolvocaceaeGenus: Volvox(Reference: wiki)There are 20 species of freshwater Volvox. Vegetative cells are somatic cells that form the shell of Volvox ball. Study the coordinated flagellar movement of the motile colonies of Volvox aureus with the immature daughter colonies represented by the dark circles, This article was most recently revised and updated by, Meet the Microbes: 5 Tiny Protozoans and Algae, https://www.britannica.com/science/Volvox, Academia - Volvox (Chlorophyta, Volvocales) as a Model Organism in Developmental Biology. This group of cells then undergoes inversion through the phialopore, resulting in the normal pattern of the colony being achieved. Sexual reproduction is oogamous. Gloeotrichia grows in a filamentous body up to ~ 2 mm in size.Photo source: wikiif(typeof ez_ad_units!='undefined'){ez_ad_units.push([[250,250],'rsscience_com-leader-2','ezslot_21',112,'0','0'])};__ez_fad_position('div-gpt-ad-rsscience_com-leader-2-0'); The Natural History of Model Organisms: From molecular manipulation of domesticated Chlamydomonas reinhardtii to survival in natureVolvox, one of the 7 Wonders of the Micro World by Wim van Egmond. There are some 20 freshwater species of Volvox which prefer to live in colonies with up to 60,000 cells by making a gelatinous wall. Volvox is a polyphyletic genus of chlorophyte green algae in the family Volvocaceae. The oogonial cell enlarges considerably and discards its flagella and protoplasmic connections with the neighboring cells. . Its multiplication is so frequent and abundant that the water of ponds becomes green (water bloom). Each coenobium is an ellipsoid or hollow sphere body with exactly marked delicate mucilage definite layer. . Other than flagellated somatic cells, a mature Volvox colony also contains reproductive germ cells. Each vegetative cell has two flagella and is attached to each other with cytoplasmic strands. Douglas Coupland Generace A. Nejnovj romn autora kultovn Generace X" ns zavd do blzk budoucnosti, kdy na Zemi vyhynou vechny vely. Each cell measured about 16.25 m in length. Within this letter to the Royal Society of London are descriptions of an organism thought to be the Volvox. The decision depends on the environmental conditions. if(typeof ez_ad_units!='undefined'){ez_ad_units.push([[250,250],'biologyeducare_com-banner-1','ezslot_0',103,'0','0'])};__ez_fad_position('div-gpt-ad-biologyeducare_com-banner-1-0');You might also read: Bryophyta: Characteristics and Classificationif(typeof ez_ad_units!='undefined'){ez_ad_units.push([[250,250],'biologyeducare_com-large-leaderboard-2','ezslot_3',104,'0','0'])};__ez_fad_position('div-gpt-ad-biologyeducare_com-large-leaderboard-2-0'); Volvox occurs in the colony because it is a coenobial form (hollow ball) like a structure. The photosynthetic colonies are usually organized so that cells with larger eyespots are grouped at one side to facilitate phototaxis (movement toward light) for photosynthesis, and the reproductive cells are grouped at the opposite side. [In this image] A daughter colony is turning itself inside out so the flagella will be orientated towards the outside of the cell.Photo source: microscopy-uk.org.ukif(typeof ez_ad_units!='undefined'){ez_ad_units.push([[250,250],'rsscience_com-leader-1','ezslot_18',109,'0','0'])};__ez_fad_position('div-gpt-ad-rsscience_com-leader-1-0'); When the parental colony ruptures and dies, these daughter colonies escape. They can be dioecious or monoecious. The base of the flagella bears single cup-shaped chloroplasts. An ovum is produced inside the oogonium and spermatozoa are produced inside the antheridium. Volvoxes are free-floating single-cellular algae but typically stay together as spherical colonies (or balls) of 500-50,000 cells. A Volvox cell is run of the mill of the Chlamydomonas type in structure (with the exception of a couple of like V. rouseletti and V. globator, which . Volvox is not an individual but an association of a number of similar cells, of which each functions like an independent individual and carries out its own nutrition, respiration, and excretion and shows no cooperation between the cells in these functions. The second division is also longitudinal but at a right angle to the first division, forming four cells. The somatic cells of a Volvox colony each feature two flagella (whiplike appendages), several contractile vacuoles (fluid-regulating organelles), a single chloroplast (the site of photosynthesis), and an eyespot used for light reception. During spring, the surface of the water in which Volox occurs looks green. Volvox belongs to the class Chlorophyceae due to the presence of chlorophyll. The coenobium is an empty circle of adhesive substance. Monoecious colonies have both male and female reproductive organs and are hermaphrodites. They reproduce both asexually and sexually. In V. campensis the zygote nucleus divides meiotically and forms four nuclei, three of them degenerate and one survives: The survived nucleus accompanied by cytoplasmic contents escapes from the vesicle. Hence they are called rolling algae. Mature sperm cells detach from the parent colony and swim towards egg cells. As autotrophs, they contribute to the production of oxygen and serve as food for a number of aquatic organisms, especially the microscopic invertebrates called rotifers. After inversion, daughter colonies keep growing, which are like many miniature versions of the parent. Volvox can grow to 500 micrometers in diameter which means that it is possible to see them without a microscope when fully grown. It was originally described by Carl Linnaeus in his 1758 work Systema Naturae. They are an important part of the aquatic ecosystem as primary producers. There are around 500 to 60,000 cells in each colony of volvox. Under favorable conditions, the inner wall layer extrudes out in the form of a vesicle and surrounds the protoplast of the zygote. Each gonidium cell divides repeatedly and produces more and more daughter cells. In this case, all cells are held together to form a new daughter colony. If a pond dries or freezes, then the dormant stages can survive until better conditions for growth return. Volvox, genus of some 20 species of freshwater green algae (division Chlorophyta) found worldwide. The young daughter colony turns itself out by inverting through the phialopore. Cell division continues and finally, they form a small spherical daughter colony, which is suspended from the parental inside surface. Some species of Volvox e.g., V. globator are monoecious or homothallic (Fig. Hypnozygote can stay at the dormant or resting stage for a period of time. Sexual reproduction is by formation and fusion of male and female reproductive cells known as spermatozoa and ova respectively. Neighbouring cells are often joined together by strands of cytoplasm, which enable cell-to-cell communication, and the colony moves through water by the coordinated movement of the flagella. Freshwater green algae that forms spherical colonies with thick cytoplasmic connections between individual cells. Some cells from the posterior side of the coenobiumbecome reproductive. Each coenobium has a definite anterior and a posterior end. Lastly, the pheromone may also be given off if the Volvox is wounded. Each cell is surrounded by a thick mucilaginous wall, forming a gelatinous layer that holds the hollow ball together. Volvox is a genus of green algae containing around 20 species of freshwater algae. Volvox species are either dioecious or monoecious. Volvox shows an advanced oogamous type of sexual reproduction which takes place by the formation of antheridia and oogonia. Thus, as many as 2-4 generations of imprisoned daughter colonies may be seen in one original parent colony, especially in V. africanus.