Biology Pamphlets Volume 571 (Paperback)

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. 1895 Excerpt: ...and their common characters of true vessels, the so-called perianth, and elongated micropyle, may have been attained independently as readily as was heterospory; but the combination of characters in common does not seem to justify such a disposition of them, and the three genera had better be regarded as of common derivation, wonderfully diversified by ancient separation, isolation, and extreme conditions. Approaching the subject from the historical standpoint, the great group Cordaites seems to be the first with sufficient data to justify consideration. The structure of the vascular bundles, especially those of the leaves, is said to suggest those of conifers, cycads, Isoetes, and Ophioglossum; and the sporophylls are organized into a strobilus, a character common to pteridophytes and gymnosperms. But such characters can be used only as cumulative testimony. In such evidences as we have of the structure of the male gametophyte, however, we obtain some valuable suggestions. Within the mature microspore there appears a considerable group of polygonal cells. In living groups of gymnosperms, so far.as investigated, there is no such structure; and if we look to pteridophytes for suggestion, we are constrained to believe that this group of cells is either prothallial or sperm mother cells. In either event, it would represent a condition of things much nearer pteridophytes than is shown by any living seed plant. In view of the discovery of spermatozoids in Cycas, Zamia, and Ginkgo, taken in connection with the peculiar structure of the male gametophyte just described, I am of the opinion that the Cordaites also developed spermatozoids. With either hypothesis as to the nature of the cells developed within the microspore of Cordaites, in seeking for the pteridophyt...