FECUNDATION IN THE VEGETABLE KINGDOM. 93 



row of cells. In Spbseroplea the whole contents of the cells 

 of some adult individuals condense into large green spores, 

 as yet without a coat ; while those of different individuals 

 give rise to myriads of slender spermatozoids, moving* by 

 means of a pair of cilia fixed at the narrow end. The latter 

 escape from the parent cell through a small perforation which 

 now appears, enter the spore-bearing cells of the fertile plant 

 through a similar perforation in them, play around the 

 spores, and at length one or more of them drives its pointed 

 extremity into their naked surface ; after which, fertilization 

 being accomplished, a thick coat of cellulose is deposited to 

 complete the spore. " Cohn does not consider that observa- 

 tions justify his assuming a direct penetration of the sperma- 

 tozoids into the primordial spore-cell. It rather seemed to 

 him as if they attached themselves on the outside of the 

 spore, and were finally converted into mucilaginous glo- 

 bules." 



Reproduction by conjugation of course had long been 

 familiarly known in the lower Algce. But it was questioned 

 whether this was really analogous to sexual reproduction, 

 since what appeared to be similar spores are often formed of 

 the contents of a single cell without conjugation. Areschoug 

 shows that these are abortive spores, incapable of germina- 

 tion ; while those which result from actual conjugation will 

 grow into new plants, without further metamorphosis ; Vau- 

 cher's old observations to this effect having been confirmed 

 by Braun and Pringsheim. 



That in the Fucacece or olive-green AlgcB the large spores 

 are fecundated by spermatozoids, produced in antheridia, 

 was demonstrated by Thuret in the year 1850. And in more 

 recent memoirs he has shown that the fertilization takes 

 place through direct contact of the spermatozoids with the 

 naked surface of the unimpregnated spore, then having only 

 a protoplasmic coating ; and that these spores will not de- 

 velop nor hardly acquire a cell-wall unless so fertilized. His 

 experiments upon dioecious species are j^erfectly decisive 

 upon these points. He observed the lively spermatozoids 

 playing over the surface of the still naked spore, fix them- 



