APOSPORY AND APOGAMY 305 



Thus, in certain Ferns the prothalli may arise by direct 

 budding from the leaves or sporangia, without the formation 

 of spores (apospory), a condition that has been experimentally 

 induced in a variety of the Lady Fern (Athyrium filix-fcemina) 

 by pinning detached segments of the fronds on damp sand. 

 In other cases the sporophyte develops vegetatively from the 

 prothallus without the intervention of sexual organs (apogamy). 1 



ft 



FIG. 170. Small part of a frond of Asplenium bulbiferum, showing the 

 vegetative production of new plants (about half natural size). 



Vegetative multiplication of the sporophyte is not infrequent, 

 new plants arising from buds formed on the surface of the fronds, 

 as in the commonly cultivated Asplenium bulbiferum (Fig. 170). 

 In the normal life-cycle, of Bryophyta and Pteridophyta 

 alike, the spore is the starting-point of the sexual, and the 

 oospore of the asexual, generation. The spore mother-cells 

 almost invariably give rise to four spores, after undergoing two 

 successive nuclear divisions. The nuclear changes involved 

 differ, however, in several important respects, from those observed 

 in the ordinary vegetative divisions of the plant (cf. p. 21 et seq.). 



1 This is analogous to the loss of sexuality observed among Fungi 

 (cf. pp. 236, 245). 

 2O 



