70 VASCULAR CRYPTOGAMS 



the substitutionary growths which accompany the arrest of spore-forma- 

 tion are restricted to the sporanges themselves. These are replaced by 

 ' pseudo-bulbils ' of a pear-like form, presenting but little resemblance to 

 ordinary prothallia, but demonstrating their oophytic character by pro- 

 ducing antherids. In other examples the prothalloid growths are by no 

 means restricted to the sporange ; they may either arise from the sorus 

 itself, or may appear at points quite distinct from the sori, and even on 

 fronds which bear no sori at all. There is here a distinct transition from 



arch 



FIG. 47. Apogamous shoot of Pteris serrulata, on the 

 under side ot the prothallium/ ; b, first leaf; z>, apex of 

 stem ; iv, rudiment of first endogenous root ( x 80). 

 (After de Bary.) 



FIG. 48. Prothalloid growth of Poly- 

 stichum angulare Willd. var. pul- 

 cherrima, originating from surface 

 of frond ; arc/i, archegone ( x 10). 

 (After Bower.) 



sporophyte to oophyte without the intervention of spores. Compara- 

 tively little is known about the oophyte generation in the Hymeno- 

 phyllaceae, but it would appear as if apogamy were a very common, 

 perhaps even normal occurrence in some species of Trichomanes (Sm.) ; 

 and here the two phenomena have even been observed on the same indi- 

 vidual, the oophyte and sporophyte generation succeeding one another 

 without the production of either spores or sexual organs. 



The fertilised oosphere or .oosperm becomes immediately invested 



