164 THE EVOLUTION OF SEX. 



IV. Parthenogenesis in Plants. — The passive bias is so strong in plants, 

 that it is easy to understand the rarity of parthenogenesis. The egg-cell which 

 develops of itself must retain the stimulus which the male element in other cases 

 supplies. It is natural, then, that what predominates in the active rotifers 

 should be uncommon in the sleeping plants. In some of the flowering plants, 

 what look like parthenogenesis has repeatedly been described, especially in 

 regard to a native of New Holland, known as Ccelebogyne. When cultivated in 

 Europe, the male flowers degenerate, and according to Braun and Hanstein 

 disappear. Yet fertile seeds are produced. Karsten found, however, that 

 stamens often persisted ; while Strasburger has shown that what developed 

 were not true egg-cells, but adventitious growths from cells outside the embryo- 

 sac. The same is true of some other cases. Dr. A. Ernst has recently 

 described what he calls true parthenogenesis in a Menisperm found by him in 

 Caracas, and named Disciphania Ernstii. "Female plants, which bore no 

 male flowers, and which were grown perfectly isolated where there was no 

 possibility of the access of pollen from another plant, produced in three succes- 

 sive years an increasing number of fertile fruits. ' ' 



In the lower plants, however, there is no doubt on the subject. Partheno- 

 genesis frequently occurs as one of the stages in the degeneration of sexual 

 reproduction. It has been casually observed of a species of the stonewort 

 (C/iara), 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 (Saprolegnicz and Peronosporece). 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 a sort of 

 protective sheaths. His series may be briefly summed up. 



1. In Pythium, the male organ discharges most of its protoplasm into the 



the female, — the usual story. 



2. In Phytophthora, only a very small portion is thus given, and we may 



almost say asked, for there are curious demand and supply arrange- 

 ments 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 Saprolegnicr, there are indeed the usual antheridia or male 



organs, which are directed toward 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. But 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 degenerate the 

 sexual reproduction, and all traces of it is often lost. The fungus fertilizes itself 



