. Plant life, considered with special references to form and function. Plant physiology. 214 PLANT LIFE. are often produced in great profusion, especially by the fungi, the mosses, the ferns, and the seed plants. 308. Form and structure.âTheir form is exceedingly various. Many are spherical or ovoid, while some are cylin- drical or even needle-shaped (figs. 213, 228, 271). Irregular forms, also, are not uncommon. In structure spores are usually only single cells, specialized. Each is a nucleated mass of protoplasm surrounded by a cell-wall which may be either thin or thick, according as the sp
. Plant life, considered with special references to form and function. Plant physiology. 214 PLANT LIFE. are often produced in great profusion, especially by the fungi, the mosses, the ferns, and the seed plants. 308. Form and structure.âTheir form is exceedingly various. Many are spherical or ovoid, while some are cylin- drical or even needle-shaped (figs. 213, 228, 271). Irregular forms, also, are not uncommon. In structure spores are usually only single cells, specialized. Each is a nucleated mass of protoplasm surrounded by a cell-wall which may be either thin or thick, according as the spore is destined to immediate growth, or, as a resting spore, to endure for a time unfavorable conditions. In some cases the wall of even the ' ',^ thin-walled spores has two layers, a ^ <A condition which is almost universal â¢$ among resting spores. AVhen the wall is so differentiated the inner layer is delicate, rarely thickened, extensible, and composed of more or less unaltered cellulose. The outer layer is often irregularly thickened, so that its surface is covered with Fig. of a mature ridges, warts, spincs, or bosscs of 271, r^p. spor^ol Pnulariaj,M«Hjcra.^^^-^^^^ g^j.^^ ^^^^^ ^^^^ ^_^g It is brittle, as compared /;, the cavity of the cell (contents not shown); it, the true wall; /' orirv \ the first, c the second, d the j99/- Ss'rp;pma^V,?'Tand5with the inner coat, and is usually have a prismatic structure. Mae- i i j. j â ⢠j_ â nified about 50 diam. - Aftir niorc Or Icss altered m composition from its original cellulose nature. A third layer (the epispore) is sometimes present, but this is not produced by the cell which it surrounds. It is added from the outside, being derived from the pirotoplasm sur- rounding tlie spores after they are formed * (fig. 209). This form of spore is common among the fern allies. * protoplasm often conies from the disorganization of some of the cells arottiul the chamljcr in which the sptores Please
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