APOSPORY AND APOGAMY 



305 



Thus, in certain Ferns the prothaUi may arise by direct 

 budding from the lea\es or sporangia, without the formation 

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

 induced in a \-ariety of the Lady I-'ern {Atliyn'iiin filix-fccmina) 

 by pinning detached segments of the fronds on damp sand. 

 In other cases the sporophj'te develops vegetati\'el\' from the 

 prothallus without the intervention of sexual organs (apogiitnv)} 



Fig. 170. — Small part of a frond of Asplenium biilbiferum, showing the 

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



Vegetati\'e multiplication of the sporophyte is not infrequent, 

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

 as in the commonlv culti\"ated Asplenium hitlbifcrnm (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 in\-ariably give rise to four spores, after undergoing two 

 successive nuclear di\-isions. The nuclear changes involved 

 differ, however, in se\'eral important respects, from those observed 

 in the ordinary vegetati^•e 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). 

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