. Botany for high schools and colleges. Botany. 396 BOTANY. is in nearly all the class essentially like the ones described. The exceptions, which are in the order Gnetacese, will be de- scribed further on. It may be pointed out here that in pass- ing up through the three orders of the class, the pollen sacs, which in the first resemble sporangia, become more nearly like the anthers of the Monocotyledons and Fig. 285. Fig, 286. FiQ. 287. Fig. 985.—A, pollen grains of Biota orientMis before their escape from the pollen eac ; 7., fresh; II. and III,, after lying In water, the extin
. Botany for high schools and colleges. Botany. 396 BOTANY. is in nearly all the class essentially like the ones described. The exceptions, which are in the order Gnetacese, will be de- scribed further on. It may be pointed out here that in pass- ing up through the three orders of the class, the pollen sacs, which in the first resemble sporangia, become more nearly like the anthers of the Monocotyledons and Fig. 285. Fig, 286. FiQ. 287. Fig. 985.—A, pollen grains of Biota orientMis before their escape from the pollen eac ; 7., fresh; II. and III,, after lying In water, the extino, c, having been stripped off by the swelling of the intine, i; the protoplaBmic conteiitp are seen to consist of two cells, a large nucleated one, and a smaller one. B, pollen grain=i of Finus pinasfer^ before their escape Irom tlie pollen sac; e, extine, witli iis vesicular protru- sions, bi; IV., side view ; Fi, dorsal view—the protoplasmic contents are divided similarly to those in A. Magnified.—After Sachs. Fiir. 286.—A, a pollen grain of Cupressua eempervirerts, showing the envelopes (ex- tine and intine), and the rudimentary prothallium as a small cell cut off from the cell contents. B, a germinating pollen grain ; e, the fragments of the ruptured and exfoliated extine ; i, intine ; tp, the base of the pollen tube. X 400.—After Schacht. Fig. 287.—Pollen grains of Ceratozamia longifolia. A, before germination ; y, a three-celled body, the rudimentary prothallinm. B, a germinating pollen grain ; e, the ruptured extine; ps, the pollen tube ; y, rudimentary prothallium. Magnified. —After Juranyi. 508.—The pollen grains, like the male flowers themselves, are essentially alike, although differing considerably in ex- ternal appearance. The vesicular protrusions of the ex- tine (II, Figs. 285, B, and 381, B), which are common in certain genera of the order Coniferm, at first sight hide the close similarity which exists between the pollen grains in many cases. (C
Size: 2138px × 1169px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1888
