. Botany of the living plant. Botany. 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, li
. Botany of the living plant. Botany. 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 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 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 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. Please note that
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1919
