Thorn — Fertilization in Aspidium and Adiantum. 289 



of '■^ composite plant,'' or a true case of polyspermy. The 

 presence of a number of spermatozoids in the neck of the 

 archegonium or even in or upon the egg itself is common, 

 and has been many times described. But there does not seem 

 to be any positive evidence that more than one spermatozoid 

 actually unites with the egg — or should such cases occur, that 

 the embryos so formed would develop into ferns. Lowe ac- 

 cepts the theory of polyspermy, but bearing in mind that 

 the fertilized e^cr is a sins^le cell, and as such should act as a 



CO o ' 



unit, the resulting hybrid, if it reached maturity at all, would 

 be expected to show uniform characters. It is, however, en- 

 tirely possible that two such embryos as shown in figure 49 

 could fuse to produce a single stem so that their individuality 

 would be, apparently at least, lost. In fact the very closeness 

 of the archegonia to each other would make such a result 

 easily possible and rather difficult to avoid without the crowd- 

 ing and dwarfing of both or the actual destruction of one. 



The Spermatozoid. 



Before attempting to discuss the process of fertilization 

 we must first consider the gametes separately. Belajeff 

 ('97) gives the following as general for the Filicineae: " Das 

 reife vollig entwickelte Spermatozoid besteht in seinem hin- 

 teren Theile aus eiuem ziemlich dicken spiralformigen Chro- 

 matinkorper der von einer diinnen Plasmahiille umgeben 

 ist." — '< Das vordere Ende des Spermatozoidenkorpers hat 

 eine bandartige Form, reagirt wie Plasma und scheint gewis- 

 sermassen eine Fortsetzung der Plasmahiille des Kernes dar- 

 zustellen." He also notes that it carries with it a cytoplasmic 

 vesicle or remnant at its posterior end. In my preparations 

 the ripe spermatozoid consists (figs. 4, 4a) of a large nuclear 

 portion tapering from a blunt end behind to a slender but not 

 sharp point forwards and thrown into from two to three turns 

 of a spiral. The number of turns depends to a large extent 

 upon whether the spermatozoid is in motion or at rest, free 

 or crowded together with others into the neck of the arche- 

 gonium. At the pointed end of the nuclear portion I could 

 determine by careful staining about one and a half short turns 

 of the spiral which contain no chromatin and must be regarded 



