. Botany of the living plant. Botany; Plants. FILICALES 497 The origin of a sporangium is by outgrowth of a single < ell of the receptacle, which undergoes successive segmentations as illustrated in Fig. 388. 1-3. A tetrahedral internal cell is thus completely segmented off from a single layer of superficial cells constituting the wall. The Conner undergoes fun segmentation to form a second layer of transitory nutritive cells called the tapetum (Fig. 388, 6-12), subsequently doubled by tangential fission (Fig. 389,1).. Fig. 389. Later stages of development of the sporangium of D
. Botany of the living plant. Botany; Plants. FILICALES 497 The origin of a sporangium is by outgrowth of a single < ell of the receptacle, which undergoes successive segmentations as illustrated in Fig. 388. 1-3. A tetrahedral internal cell is thus completely segmented off from a single layer of superficial cells constituting the wall. The Conner undergoes fun segmentation to form a second layer of transitory nutritive cells called the tapetum (Fig. 388, 6-12), subsequently doubled by tangential fission (Fig. 389,1).. Fig. 389. Later stages of development of the sporangium of Dryopteris b'ilix-mas. (After Kny.) The tetrahedral cell which still remains in the centre, having grown mean- while, undergoes successive divisions till twelve sporc-mothcr-cclh are formed (Fig. 389, 2-7). These become spherical, and are suspended in a liquid which, together with the now disorganised tapetum, fills the enlarged cavity of the sporangium. Each'spore-mother-cell then divides twice to form a Spore- tetrad: in this process, just as in the formation of pollen-grains and other spores, the number of chromosomes is reduced to a half. Finally the resulting cells separate on ripening as individual spores, each covered by a protecting wall, rugged and dark brown at maturity. Owing to the absorption of the liquid contents of the sporangium the separate spores are dry and dusty, and. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bower, F. O. (Frederick Orpen), 1855-1948; Wardlaw, C. W. (Claude Wilson), 1901-. London, Macmillan and Co. , ltd.
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