Spermatogenesis and Fecundation of Zamia - Softcover

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated.1901 Excerpt: ... responds very closely to that occurring in Cycas, Ginkgo, and the Coniferaj. The nucleus of the central cell in preparing for division evidently goes through changes similar to those described by Murrill in Tsuga canadensis, and it would be interesting to know if the same unique method of spindle formation occurs in Zamia also. The accumulation of highly granular cytoplasm in a conspicuous mass below the nucleus of the central cell, as described by Murrill in Tsuga, is uniformly found in stages immediately preceding division in Zamia. The synapsis condition observed by Murrill in an early prophase of the division in Tsuga is also of common if not normal occurrence in Zamia, so that it would seem probable that the spindle formation in Zamia may be similar to that of Tsuga. It is interesting to observe that the spindle formed in this division is strikingly blunt-poled, as observed by Ikeno in Gycas (65) and Btockman in Pinus (16). Before fecundation the canal cell breaks up and loses its identity, only traces of it being occasionally found at the time of fecundation. After the division giving rise to the canal cell is completed, the lower nucleus which forms the oosphere travels from the apex of the cell downward toward the center and takes a position slightly below the middle of the cell, where it remains until fecundation takes place. It is usually spherical or slightly elliptical, and its contents are much less dense than the surrounding cytoplasm of the egg cell, with which it forms a marked contrast. The mature egg cell is usually elliptical or slightly reniform and is about 3 mm. in length and from 1 to 1.5 mm. in width. The nucleus is very large, being about 553 f i long and 467 / in diameter. It is plainly visible to the unaided eye in stained section...