TAXONOMY 
291 
wet season, and, moving through the water, are drawn by a chemo- 
tactic influence to the archegonia of another prothallus, pass down 
the neck canals of these and fuse with the ova, fertilizing them. 
The fertilized egg or oospore divides and redivides and soon becomes 
differentiated into stem-bud, first leaf, root, and foot. The foot 
Fig. 158. — Equisetum arvense. P, sterile branch; P 1 , fertile branch with 
strobilus, or cone; R, rhizome, (underground); T, cross-section of cone, showing 
insertion of sporophylls in a whorl; N, N 1 , sporophylls with pendant sporangia; 
S, S 1 , S 2 , spores with coiled elaters (el). (Gager.) 
obtains nourishment from the prothallus until the root grows into 
the soil, when it atrophies, and the sporophyte becomes independent. 
Unequal growth and division of labor continue until a highly differ¬ 
entiated sporophyte results, the mature “fern plant.” 
