Morphology of angiosperms Volume 2; (Morphology of spermatophytes. Part II)

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. 1903 Excerpt: ...of prothallus, we must trace the origin of the triple nuclear fusion which precedes its development"; and if it is a modified embryo "we have to account for the interference of the lower polar nucleus with the act of fertilization, and for the subsequent development of a body unlike a normal embryo." Her suggested interpretation of the phenomenon is that the fusion of the male nucleus with the micropylar polar nucleus, an undoubted female nucleus, both containing the reduced number of chromosomes, is a typical sexual union; but that the antipodal polar nucleus, with its vegetative character, and indefinite and usually increased number of chromosomes, is a disturbing factor, and the result is not a normal embryo but a small and short-lived mass of tissue. She aptly cites the experiments of Boveri13 with sea-urchins, in forcing more than one spermnucleus to unite with a single egg-nucleus and producing monstrous larval structures. "The presence of the third nucleus, therefore, with its redundant chromosomes, serves to secure the degeneracy of the resulting tissue." This means, of course, that the endosperm is a degenerate embryo, and that the triple fusion is a true sexual union whose normal result has been interfered with by the presence of a non-sexual nucleus in the combination. It is impossible to solve such a problem by a discussion of the data we possess. The phylogeny of the endosperm must be traced, and the place of the polar fusion and of the triple fusion in its history determined before opinions cease to differ as to its morphological character. In view of such facts as we have, however, we are inclined to hold with Strasburger that the endosperm of Angiosperms is a gametophytic structure, and that the polar fusion and the ...