176 THE EVOLUTION OF SEX. 



Parthenogenesis frequently occurs as one of the stages in the degeneration 

 of sexual reproduction. It has been casually observed of a species of 

 the stonewort {Chard), that when grown in certain waters the male 

 organs disappear, yet the plants continue multiplying. More interesting 

 are the Fungi. To illustrate sexual degeneration, De Bary gives a series 

 from Fungi like those which kill the salmon and potato {Saprolcgniic and 

 Peronosporecr). What happens first, is the degeneration of the male organs. 

 The katabolic sex from beginning to end is the more unstable. The male 

 function goes first, but the form remains after the reality has ceased. 

 After a while, that is in related species, the form goes too. Sometimes 

 the function is changed, and the male organs become sort of protective 

 sheaths. His series may be briefly summed up. 



(i.) In Pythiiim, the male organ discharges most of its protoplasm into 

 the female, — the usual story. 



(2.) In Phytoplitliora, only a very small portion is thus given, and we 

 may almost say asked, for there are curious demand and supply 

 arrangements and compulsions between the male and female organs 

 in these Fungi. 



(3.) In Peronospora, there is no perceptible passage of protoplasm from 

 male to female, though, without going back to the "aura 

 seminalis," we may allow the possibility of subtle osmosis. 



(4.) In some Saprolegiiicv, there are indeed the usual antheridia or male 

 organs, which are directed towards the female organs, but do not 

 open. The " explosive" character is diminishing. 



(5.) In others, the male organs never get near the female. 



(6.) In others, there are no male organs at all, but the female cells 

 develop as usual. 



Parthenogenesis is thus reached, as the result plainly of a degenerative 

 process. We can follow the story further, however, forestalling for the 

 moment the subject of the next chapter. The male organ has degenerated, 

 we have seen, while the female organ holds on its course. Put this is not 

 always so ; in many cases it follows suit, and asexual reproduction 

 remains. 



Now why should these Fungi among plants exhibit numerous instances 

 of parthenogenesis ? The more intimate the parasitism, the more degener- 

 ate the sexual reproduction, and all trace of it is often lost. The Fungus 

 fertilises itself from its host. In the Fungus on the coffee plant, for 

 example, the stimulus of fertilisation is replaced as it were by an "essence 

 of coffee." 



Male parthenogenesis, paradoxical as it sounds, is really exhibited 

 among lowly alga:. Thnt is to say, a small spore (or male-cell) which 

 normally unites with a larger and more quiescent one (or female-cell), may 

 occasionally start developing on its own resources. The result, however, 

 is poor enough. As those spores are on the border line between 

 asexuality and differentiated sex-elements, the retention of a vegetative 

 power of division even by the incipient male-cell is not surprising. Nor 

 must it be forgotten that the mother-spcrm-cell itself has a power of 

 parthenogenetic development. It divides, like its homologue the ovum, 

 into a ball of cells, but having none of the conservative coherence of the 

 latter breaks up into spermatozoa. It is exactly comparable to the 

 interesting Protozoon [Magospluera) which Hoeckcl saw, which did its best 

 to get beyond the Protozoa, but failed as soon as it had succeeded. A 



