Elementary botany . elementarybotany00atki Year: 1898 Fig. 269. Fig. 270. Section of ovule of white pine, int, integ- Upper portion of nucellus of white pine, ument; A- pollen chamber; />/, pollen tube; A', pollen-grain remains; spc, sperm cells; «, nucellus; m, macrospore cavity. vn, vegetative nucleus; //, pollen tube. reached its full size, and where the archegonia begin to form before it Leaves the macrosporangium. 421. Male prcthallia. T>y the time the pollen is mature the male pro- thallum is already partly formed. In fig. 255 we can see two well-formed cells. Other cells are said
Elementary botany . elementarybotany00atki Year: 1898 Fig. 269. Fig. 270. Section of ovule of white pine, int, integ- Upper portion of nucellus of white pine, ument; A- pollen chamber; />/, pollen tube; A', pollen-grain remains; spc, sperm cells; «, nucellus; m, macrospore cavity. vn, vegetative nucleus; //, pollen tube. reached its full size, and where the archegonia begin to form before it Leaves the macrosporangium. 421. Male prcthallia. T>y the time the pollen is mature the male pro- thallum is already partly formed. In fig. 255 we can see two well-formed cells. Other cells are said to be formed earlier, but they become so flattened that it IS difficult to make them out when the pollen grain is mature. At this Mage of development tin- pollen grain is lodged at the mouth of the ovule. and i> drawn up into the pollen chamber. 425. Farther growth of the male prothallium. During the summer and autumn the male prothallium makes some farther growth, but this is slow. The larger cell, called the vegetative cell, elongates by the*formation of a tube, forming a sac, known a- the pollen tube. Itiseither simple or branched, [nside of this sac the cell- of the prothallium are protected, and farther
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