. Physiological botany; I. Outlines of the histology of phænogamous plants. II. Vegetable physiology. Plant physiology; Plant anatomy. 438 angiosperms shows that in the latter the nucleus divides, but that the division stops here, no true dividing-wall being formed. 1134. Ovule of (jymiiosperms. Ttie ovule is always ortliotropous. It has an integument which is sometimes prolonged so as to form a flesly tube communicating with the nucellus. The nucellus, like that of angiosperms, contains an embryonal sac; at an early stage this is filled with endosperm, which it will be remember
. Physiological botany; I. Outlines of the histology of phænogamous plants. II. Vegetable physiology. Plant physiology; Plant anatomy. 438 angiosperms shows that in the latter the nucleus divides, but that the division stops here, no true dividing-wall being formed. 1134. Ovule of (jymiiosperms. Ttie ovule is always ortliotropous. It has an integument which is sometimes prolonged so as to form a flesly tube communicating with the nucellus. The nucellus, like that of angiosperms, contains an embryonal sac; at an early stage this is filled with endosperm, which it will be remembered is not developed in angiosperms until after fertilization. Some of the upper cells of the endosperm are rather larger than the others, elongated in the direction of the axis of the ovule, and each surmounted b}- a " rosette " of minute cells which comes between the group and the summit of the embrj'o sac. These large cells, with their rosettes, are termed cor- pusculea. These corpuscules are considered oospheres. Around them in the embryo sac there ap- pears to be nothing corresponding strictl}' to the synergidas, the an- tipodal cells, etc., observed in the angiosperms, although some ho- mologies have been pointed out. In some cases, like that figured, there is a sort of depression at the summit of the endosperm, which has been called the pollinic chamber. 1135. Contact of pollen with the ovule. As the name indi- cates, the gymnosperms are naked seeded ; no stigma or style inter- venes between the pollen and the ovule. When the divided pollen of the gymnosperm falls upon the micropyle of the ovule, It Fig. 207. PoUen-graiii of Ceratozamia longifolia. A, grain with partial partitions; B, the same emitting its tube, ps, which has ruptured the outer coat; y, minute inactive cells. (Juranyi.) Fig. 208. Longitudinal section of the nucellus of the naked ovule of Juniperus Virginiaiia. 71, nucellus; se, membrane of the embryonal sac; c, endosperm; c, cor- puscles ; p, a
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectplantanatomy, bookyea
