. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. REDUCTION—DIVISION—SPORE-FORMATION 307 of each separating pair respectively represent the chromatic material of the two parents from which the given organism arose (cf. p. 390). The importance of this phenomenon is also emphasised by the occurrence of an essentially similar method of reduction in animals. Reduction occurs in the formation of spores, not only in all Bryophyta and Pteridophyta, but also in the higher plants (Phanerogams). In the case of the Thallophj'ta the actual reduc- tion has onl}' been obs
. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. REDUCTION—DIVISION—SPORE-FORMATION 307 of each separating pair respectively represent the chromatic material of the two parents from which the given organism arose (cf. p. 390). The importance of this phenomenon is also emphasised by the occurrence of an essentially similar method of reduction in animals. Reduction occurs in the formation of spores, not only in all Bryophyta and Pteridophyta, but also in the higher plants (Phanerogams). In the case of the Thallophj'ta the actual reduc- tion has onl}' been observed in relatively few cases, but it cannot. Fig. 171.—Nuclear divisions in spore mother-cells of Nephrodium (after Yamanouchi). A, Late synapsis. B, Segmentation of chromosomes. C, Association of chromosomes. D, Equatorial plate. E, Part of a tetrad. be doubted that it takes place in all forms exhibiting a sexual process. It would appear, however, that it may be effected at various stages in the life-history, sometimes (as in Spirogyra) during the first division in the zygospore, in other cases { Fiicus) during the formation of the sexual cells. It may be noted that the latter is the customarj' stage for the occurrence of the reduction division amongst animals. The four nuclei, produced in the spore mother-cell, usually become grouped so as to form a tetrahedral figure. Each, together with part of the cytoplasm, becomes surrounded by a separate wall, the whole of the contents of the mother-cell being. 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 Fritsch, Felix Eugene, 1879-; Salisbury, E. J. (Edward James), Sir, b. 1886. London, G. Bell and sons ltd.
Size: 1814px × 1377px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjectpl, booksubjectplants
