Text-book of botany, morphological and physiological . other-cells of thespores can arise by free cell-formation. Each mother-cell is, in Aspidium Filix-mas(Fig. 268, /), provided with an evident nucleus; after its absorption (//), two newlarge clear nuclei arise (///), between which an evident line of separation is some-times to be seen. After the absorption of these nuclei which show the commence-ment of a bipartition, four new smaller nuclei appear {IV), the mother-cell splittingup into four spore-cells (T), the relative position of which varies (as is shown inFigs. VI, VII, and VIII), The
Text-book of botany, morphological and physiological . other-cells of thespores can arise by free cell-formation. Each mother-cell is, in Aspidium Filix-mas(Fig. 268, /), provided with an evident nucleus; after its absorption (//), two newlarge clear nuclei arise (///), between which an evident line of separation is some-times to be seen. After the absorption of these nuclei which show the commence-ment of a bipartition, four new smaller nuclei appear {IV), the mother-cell splittingup into four spore-cells (T), the relative position of which varies (as is shown inFigs. VI, VII, and VIII), The spore now becomes clothed with its cell-wall,which is differentiated into an endospore consisting of cellulose and a cuticularisedbrown exospore furnished with ridges {IX), and chlorophyll is formed within thespore. The spores of many Polypodiaceae are distinguished by the long periodduring which they retain their power of germination, and by the slowness of thisprocess; those of Hymenophyllacese often begin to germinate while still in Fig. 268.—Development of the spores oi Aspidium Filix-mas (XS50). Ihe Systematic Classification of Perns, as generally given in handbooks, is based arti-ficially on the form of the mature sporangium for the families, and of the sorus for thegenera; only those groups which have already been repeatedly meniiioned are accuratelyknown. It appears certain that the Hymenophyllaceae contain the lowest forms mostnearly allied to the Muscineae; the genetic relationship of the other families with theHymenophyllaceae and with one another has not yet been ascertained; but the Hy-menophyllaceae probably form the starting point for two or more series of (Filices Horti Botanici Lipsiensis) distinguishes the following families, whichI adopt with some alteration in the arrangement:— I. Hymenophyllaceae. 2. Gleicheniacese. • 5. Marattiacese (vide infra). 3. Schizaeaceae. 6. Cyatheaceae. 4. Osmundaceae. 7. Polypodiaceae. In
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectbotany, bookyear1875
