SECT. Till. 



DEVELOPMENT OF SPORES. 



337 



green leaf or marchantioid prothallus (fig. 51 D) is 

 formed. This prothallus lies flat on the ground, and 

 is furnished on the under-side with fibrous roots to fix 

 it, and supply it with food. 



Two sets of organs are subsequently developed on the 

 under-side of this prothallus ; one of these is a stalked 

 cell called an antheridium, and is situated near the 

 roots ; the other is an archegonium containing a gerni 

 cell, which is sunk in the cellular tissue. In each of the 



Fig. 51. Development of spores of Pteris serrulate : A, spore ; B, c, early stages of 

 development ; D, the prothallus with radical fibres (a, 6; and antheridia (h, h). 



antheridia, which are numerous, a cell is formed, which 

 becomes filled with a mass of mucilage mixed with 

 a number of free cells, containing a flat ribbon-shaped 

 filament, or spermatozoid, coiled in a spiral manner, 

 which, as soon as set free by the rupture of the cell, 

 revolves rapidly by means of several long cilia placed 

 close to the large end. Fig. 52 shows the globular 

 antheridium and the spermatozoids of Pteris serrulata. 

 The archegonia are fewer in number, and contain the 

 germ cell, represented in fig. 53, as viewed from above, 

 VOL. i. z 



