. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. MUSCINEM—HEPATIC^—MARCHANTIALES 35 Fig. 7, A shows the nucleus of the mother cell under- going the first division. The small size of the nuclei, and the small amount of chromation in them, make the study of the details of the nuclear division difificult here, and as there was nothing to indicate any special peculiarities these were not followed out. After the first nuclear division the daughter nuclei divide again, after which the four nuclei arrange them-. FlG. y,^Riccia trichocarpa. A, Secti
. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. MUSCINEM—HEPATIC^—MARCHANTIALES 35 Fig. 7, A shows the nucleus of the mother cell under- going the first division. The small size of the nuclei, and the small amount of chromation in them, make the study of the details of the nuclear division difificult here, and as there was nothing to indicate any special peculiarities these were not followed out. After the first nuclear division the daughter nuclei divide again, after which the four nuclei arrange them-. FlG. y,^Riccia trichocarpa. A, Section of a spore mother cell undergoing its first division, X6oo; B, section of young spore tetrad, X30D; C, section of ripe spore, X300; D, surface view of the exospore of a similar stage, X300. selves at equal distances from each other, the division walls form simultaneously between them, dividing the spore mother cell into the four tetrahedral spores. A section through such a young spore-tetrad is shown in Fig. 7, B, where one of the cells is somewhat shrunken in the processof embedding. The cell walls at this stage are very delicate and of unchanged cellulose; but as they grow older the wall soon shows a separa- tion into endospore and exospore. The latter in R. tricho- carpa, which was especially studied, is very thick, at first yellowish in colour, but deepening until when ripe it is black. Sections parallel to the surface show in this species what appear to be regular rounded pits, but vertical sections of the spore-coat show that this appearance is due to a peculiar fold-. 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 Campbell, Douglas Houghton, 1859-1953. New York, The Macmillan Company;
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