I30 



GENERAL BIOLOGY 



developed, and the sporophyte phase is, save in its origin, 



Fig. 78. Fern embryos, a, after the first division into two cells; 

 b, an embryo showing the begmnings of root (r), stem (5) and 

 leaf (/); c, an older embryo, the leaf tip turning upward, vas- 

 cular bundles {v), developing; /, foot. 



exceedingly different. The comparison of sporophytes will, 



therefore, be more readily made if it 

 be a comparison of early stages. 



The sporophyte. — The fertilized egg 

 divides (fig. 78 a) and produces a 

 mass of cells within the walls of the 

 archegonium. From this cell mass 

 there are early differentiated a num- 

 ber of parts, one of which clearly cor- 

 responds to the foot of such sporo- 

 phytes as we have seen hitherto, it 

 being a food absorbing organ im- 

 mersed in the tissues of the parent 

 gametophyte (fig. ySf). From the 

 remainder (which corresponds only in 

 a general way to the sLalk) root and 

 leaf develop, the root extending down- 

 ward into the soil, branching and 

 developing rhizoids for independent 

 foraging there, the leaf passing out 

 between the lobes at the apex of the thallus and turning up- 

 ward to the light and expanding, taking tip its proper 

 work of carbon dioxide reduction (fig. 79). Thus the 



Fig. 79. The fern sporo- 

 phyte, in the first leaf, 

 but still attached to the 

 parent gametophyte. 



