SEXUAL REPRODUCTION ((EDOGONIUM) 223 



the first stages of development by mere pricking. Moreover, 

 in plants, fertilisation sometimes stimulates other cells near the 

 egg to develop into embryos (cf. p. 372). 



The fertilised eggs, or oospores, develop thick protective walls 

 and fatty pigmented contents and, as the filaments containing 

 them die away, sink to the bottom of the water. Here they pass 

 through a prolonged resting period, and, should the pond dry 

 up, may be dispersed by the wind. In the few cases in which 

 their germination has been observed, they gave rise to three or 

 four ordinary zoospores, which were set free by the bursting of 

 the thick membrane. 



The sexual organs are arranged in various ways in the different 

 species of (Edogonium, male and female sometimes occurring in 

 the same filament (monoecious forms), sometimes in different 

 filaments (dioecious forms) ;, in the latter case the male plants 

 often consist of only a few cells (dwarf males, Fig. 120, ~B,d.m.), 

 and arise from special smaller zoospores which become attached 

 to the female plant, on or near an oogonium. 



It will be evident that (Edogonium exhibits considerable 

 specialisation in its methods of multiplication, and not the least 

 conspicuous feature is the division of labour manifest in the 

 oogamous sexual reproduction. Owing to its stationary character, 

 the egg can possess the greater bulk which a more adequate 

 provision of food-material for the benefit of the next generation 

 necessarily entails (cf. p. 220). Since the spermatozoids con- 

 tribute nothing to this food-supply, they can be correspondingly 

 smaller, and therefore, without additional strain on the organism, 

 produced in larger numbers, whereby the chance of fertilisation 

 occurring is greatly increased. The probability of fusion between 

 the two gametes is, moreover, doubled by one of them remaining 

 stationary. The greater certainty of sexual union admits of a 

 corresponding decrease in the production of eggs, which will 

 afford as many offspring as would a larger number of motile 

 female gametes. These remarks apply with equal force to all 

 plants in which oogamy occurs. 



The oogonia and antheridia of Vaucheria are produced near 

 one another as outgrowths of the main filament or of short lateral 

 branches, from which in either case they become separated by 

 a septum (Fig. 120, E). Their relative positions are very 



