350 



BOTANY OF THE LIVING PLANT 



In the relatively simple case ot Neplnodium pseudo-inas, var. polydacty!a 

 a young sporophyte is produced as a direct outgrowth from the prothallus. By 

 a careful examination of the bud-forming tissue it has been found that the bud 

 is preceded by a sort of irregular fertilisation. The nucleus passes from one 

 cell through a pore in the cell-wall into the next cell. There it fuses with the 

 nucleus of the invaded cell (Fig. 294). Doubtless there is here a doubling of 

 the chromosomes, as m normal fertilisation ; and such a cell, like a false 

 zygote, may serve to initiate the sporophytic bud. The process has been 

 styled pseudomi.ris to suggest a comparison with sexuality, while marking its 

 distinctness from it. 



In other cases careful investigation has shown that a gametophyte may 

 be diploid. Transition from one generation to the other nray then be repeated. 



Fig. 293. 



Pteris crelica ; prothallus seen from below, bearing an apoganious bud derived not by 



fertilisation but by direet growth from the cushion. (After Dc Baxy.) 



while uniformity of chromosome-number is maintained throughout. This 

 is seen in Atliyrimn filix-foemina, var. clarissiiua, where the number is 90, 

 approximately that for the normal sporophyte of that species. The same is 

 the case for certain plants of Mcinilia Drummondii, which are diploid through- 

 out, with 32 as the number. It is probable that the converse is the case for 

 Lastraea pseudo-mas, var. cristaia (Fig. 295), for the chromosome-number 

 throughout was found to be varial:)le, from 60 to 78, whiie in that species the 

 normal number for the sporophyte is 1.14. Not only do such cases show that 

 the usual chromosome-cycle may be departed from, but also that the external 

 characters are not directly dependent upon the chromosome-number. 



The cycle of life of a Fci-ii sho\vs more clearly than that of anv of 

 the Vascular Plants hitherto tlescribed the antithesis of the two 



