. The classification of flowering plants. ment with a long narrowmicropyle, a large mass of nucellus above the megaspore, and aconspicuous nucellar beak projecting into the micropyle abovethe pollen-chamber (fig. 11, C). Hirase, who has recentlyworked out the gametophyte stage in the life-history of Ginkgo,finds that the pollen-chamber is organized early in May, soonafter the maturing of the pollen, and that about the time ofpollination it is full of liquid; also that the chamber is formedfrom the development of the external tissue of the beak, theinner tissue becoming disorganized. His accoun
. The classification of flowering plants. ment with a long narrowmicropyle, a large mass of nucellus above the megaspore, and aconspicuous nucellar beak projecting into the micropyle abovethe pollen-chamber (fig. 11, C). Hirase, who has recentlyworked out the gametophyte stage in the life-history of Ginkgo,finds that the pollen-chamber is organized early in May, soonafter the maturing of the pollen, and that about the time ofpollination it is full of liquid; also that the chamber is formedfrom the development of the external tissue of the beak, theinner tissue becoming disorganized. His account of the development of the male gametophyte isas follows. A small lenticular cell is formed in the microspore,but soon disorganizes, and is subsequently recognisable only as acleft in the thick spore-membrane. This ephemeral vegetative 5—2 68 FLOWERING PLANTS [CH. cell appears also in the germination of the microspore inConifers, but was not found in the Cycads. A second smallcell is cut off beneath the first, and persists as a second. Fig. 11. Ginkgo liloba. A. Early stage in germination of pollen-grain; x 250. p, persistent prothallial or vegetative cell; g, generative cell; t, tube-cell. B. Later stage; s, remains of pollen-grain from which the pollen-tube has developed; jj, persistent prothallial cell, below side by side are seen thetwo male cells produced by division of the body-cell; x 110. (A and Bafter Hirase.) C. Ovule in longitudinal section; x 2^. ??t, micropyle;/, integument; ft, beaked apex of nucellus with polleu-chamber containing pollen-grains; m (lower),embryo-sac; c, collar around base of ovule; x, excretory sac. (AfterCoulter and Chamberlain.) D. Apex of embryo-sac in longitudinal section shewing oospore filled with the compact tissue of the ovule ; x 30. (After Strasburger.) E. Seed in longitudinal section shewing fleshy and hard layers of seed-coat, the latter indicated by a thick black line, the endosperm (en) and theembryo (c). vegetative cell (fig. 11
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbotany, bookyear1904
