. Botany for high schools and colleges. Botany. G YMN08PEBMJE. 397 same figure.) In all cases, unless possibly the Gnetacese fur- nish some exceptions, the pollen grains become more than one- celled before the formation of the pollen tube (Figs. 281-5- 6-7). "When the pollen grains germinateâ, send out their tubesâthey always swell up and burst the cxtine (which slips off in the Coniferse), and the intine is then prolonged into a tube, â which is continuous with the cavity of the grain, and into which the protoplasmic con- tents pass (Figs. 286 and 287). The small cells take no active
. Botany for high schools and colleges. Botany. G YMN08PEBMJE. 397 same figure.) In all cases, unless possibly the Gnetacese fur- nish some exceptions, the pollen grains become more than one- celled before the formation of the pollen tube (Figs. 281-5- 6-7). "When the pollen grains germinateâ, send out their tubesâthey always swell up and burst the cxtine (which slips off in the Coniferse), and the intine is then prolonged into a tube, â which is continuous with the cavity of the grain, and into which the protoplasmic con- tents pass (Figs. 286 and 287). The small cells take no active part in the formation of the tube, and from their similarity, both in structure and function, to the small cells in the germi- nating microspores of the Sel- aginellm, there can be no doubt that they arc to be regarded as constituting a rudimentary prothallium. 509.âThe female flower is in most cases a similar elon- gated axis, upon which are ar- ranged spirally a considerable number of phyllomes, each bearing two or more naked ov- ules. Thus in Abies pectinata the female flower is the young cone, which consists of an axis {sp, Fig. 288, B) bearing nar- row bracts (e), which, in turn, develop thick scales (s, s) upon their upper surface. The scales are at first quite small (as in A), and it is only as the cone becomes older that they grow larger. Each scale bears on its inner face two inverted ovules (.s^, Fig. 388, A). In Pimis sylvestris the structure is essentially the same as. I'ig. 288.âA, a bract, c, detached from the axis of a young cone of Abies pecUnata, with the scale, 5, bearing the ovules, ah (enlarged). B, upper part of a mature coue ; ap, axis ; c. bracts ; 5, largely developed scales, bearing the seeds on the upper surface (reduced). C, ripe scale, with two winged seeds; sa^ seed; f, wing (reduced).âAfter Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and app
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1888
