PTERIDOFHYTES 



137 



idia begin to appear very early (Fig. 116), and later the 

 archegonia (Fig. 117). If the prothallium is poorly nour- 

 ished, only antheridia appear ; it needs to be well developed 

 and nourished to develop archegonia. There seems to be 

 a very definite relation, therefore, between nutrition and 

 the development of the two sex organs, a fact which must 

 be remembered in connection with the development of 

 heterospory. 



79. The sporophyte. — This complex body is differentiated 

 into root, stem, and leaf, and is more highly organized 

 than any plant body heretofore mentioned (Fig. 118). The 

 development of this body and its three great working regions 

 must be considered separately. 



(1) Development of embryo. — The oospore, from which 

 the sporophyte develops, rests in the venter of the arche- 

 gonium, which at this stage resembles a depression in the 



Fig. 119. Embryos of a common fern (Pterin): A, young embryo, showing direction 

 of basal wall (I), and of second walls (II), which organize quadrants, each of 

 which subsequently develops into foot (/), root (w), leaf (6), and stem («); B. an 

 older embryo, in which the four regions (lettered as in A) have developed further, 

 also showing venter of archegonium (aw), and some tissue of the prothallium (pf). 

 — A after Kiexitz-Gerloff; B after Hofmeister. 



lower surface of the prothallium (Fig. 119, B). It germi- 

 nates at once, as in Bryophytes, not being a resting spore 

 as in Green Algae. The resting stage, as in the Bryophytes, 



