124 ELEMENTS OF BIOLOGY. 



this ever really happens. The fluid matter of the pollen- 

 tube, and possibly some of the minutely granular '" fovilla " 

 as well, is now transferred to the embryo-sac ; and as the 

 result of the stimulus thus imparted, one or more of the 

 embryonal vesicles is impregnated, when the pollen-tubes 

 decay. 



As regards the reproduction of the Flowerless Plants 

 (Cryptogams)^ the process varies much in different cases; 

 but in the higher forms the essential element of the process 

 consists in the production of sperm-cells or spermatozoa, and 

 a germ-cell or ovum. There are, however, some very singu- 

 lar complexities in the manner in which these essential 

 generative elements are produced, and we may notice the 

 phenomena which have been observed in Ferns : — 



The ordinary Ferns are well known to produce at certain 

 seasons what are commonly spoken of as the "organs of 

 fructification. '^ In the commoner species these take the 

 form of little rounded masses, which are generally placed 

 upon the back of the adult frond (fig. 37, A). When 

 examined microscopically, each of these spots of fructifica- 

 tion is found to consist of an aggregation of minute recep- 

 tacles or '' spore-cases," containing in their interior still 

 more minute cellular bodies or " spores." If one of these 

 spores be liberated from the spore-case, and placed under 

 favourable conditions, it germinates, giving off roots on the 

 one hand, and producing on the other hand a little cellular 

 expansion or leaf, which is termed the "prothallus" (fig. 

 37, D). This prothallus, however, is not itself developed 

 into a new fern, but it is a mere temporary or provisional 

 body, upon which are produced male and female organs 

 of reproduction. The male organs are produced upon the 

 under side of the prothallus, and they have the form of 

 minute cellular eminences, containing reproductive cells. 



in the case of the white corpuscles of the blood, render it by no means 

 unlikely that the fovilla itself reaches the embryo-sac without any neces- 

 sary rupture of the walls of this cavity or of the pollen-tube. 



