INTRODUCTION. 



^35 



substance with it. The size of the antherozoids is so inconsiderable that they 

 scarcely add appreciably to the mass of the oosphere, but yet produce a change in 

 it, one consequence of which is that it becomes invested with a firm cell-wall, and 

 then constitutes the Oospore. 



The oospore may germinate immediately and give rise to a plant resembling the 

 mother-plant, as in Fucus, or only after a certain period of rest like the zygospores, 

 and this is the usual case. But here again the oospore may on germination give 

 rise directly to a plant resembling the mother-plant, as in Vaucheria and some 

 Saprolegnieae ; or it may, after remaining dormant, produce out of its contents a 

 larger or smaller number of zoospores, each of which finally gives rise to a plant 

 like the mother-plant, as in Sphceroplea, (Edogonium, and Cystopus. In this process 

 a rudimentary alternation of generations can again be detected:— an oospore which 

 breaks up into zoospores may be compared to the sporogonium of a Moss in 



Fig. 163.— Examples of the production of oospores; A in CEdogonium ; B va. Saprolegiiia 

 (after Pringsheim) ; og the oogonium ; o oosphere; a antheridium ; ni small male plant or dwarf 

 male ; s antherozoid. 



/hich all the parts except the spores are suppressed. If we were to imagine the 

 fertilised oosphere in the archegonium of a Moss as itself producing the mother- 

 cells of the spores \ we should have something similar to one of these oospores. 

 In this case therefore the oospore is properly a many-spored fructification in 

 the same sense as the Moss-capsule ; the zoospores produced from it are true 

 spores in the sense of those of Muscinese and Ferns, and we have consequently 

 the first indication of the alternation of generations which attains its highest 

 development in those classes. The new plants which result from the direct 

 germination of the oospores, or through the medium of zoospores, have the power, 

 in most cases, of propagating non-sexually by the formation of gonidia, until at 

 length individuals arise which produce antheridia and oogonia. This non-sexual 

 reproduction iriay be compared to that of the Marchantiese by gemmae produced 

 on their vegetative body, until finally antheridia and archegonia are developed. 



^ That such an analogy is not altogether fanciful is shown by Riccia, a genus of Hepaticse, 

 the extremely simple sporocarp of which may well be compared to the oospore of an CEdogonium. 

 Pringsheim and De Bary have already pointed out this analogy (see De Bary, Die Familie der 

 Conjugaten, Leipzig 1858, p. 60). 



