. Essentials of botany. Botany; Botany. 302 ESSENTIALS OF BOTANY evident without careful examination. The pistil is the megaspore-producing leaf, or megasporophyll, and the sta- men is the microspore-producing leaf, ot miorosporojjhyll. Pines and other gymnosperms produce a large cell (the em- bryo sac) in the ovule (Fig. 218) which is the megaspore, and a pollen grain which is the micro- spore. In its development the megaspore produces an endo- sperm or small cellular prothal- lium, concealed in the ovule. The microspore contains vestiges of a minute prothallium. In the angiosperms the mega-
. Essentials of botany. Botany; Botany. 302 ESSENTIALS OF BOTANY evident without careful examination. The pistil is the megaspore-producing leaf, or megasporophyll, and the sta- men is the microspore-producing leaf, ot miorosporojjhyll. Pines and other gymnosperms produce a large cell (the em- bryo sac) in the ovule (Fig. 218) which is the megaspore, and a pollen grain which is the micro- spore. In its development the megaspore produces an endo- sperm or small cellular prothal- lium, concealed in the ovule. The microspore contains vestiges of a minute prothallium. In the angiosperms the mega- spore and its prothallium are still less developed, and the micro- spore, or pollen grain, has lost all traces of a prothallium and is merely an antheridium which sooner or later produces two generative cells. These are most easily seen in the pollen grain, but sometimes they are plainly visible in the pollen tube (Fig. 123, B). Seed-plants are distinguished from all other plants by their power of producing seeds, or enclosed megai<porangia with embryos. 384. The Sexual Generation and Relationships of the Great Groups of Plants. — On summing up Sects. 381- S83 it is evident that the sexual generation in general. i"iG. 218. Longitudinal Section tiirough Fertilized Ovule of a Spruce. p, pollen grains; t, pollen tubes; n, neck of the arcbegoniuni; II, body of archegonium with nucleus; «, embryo sac filled with Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bergen, Joseph Y. (Joseph Young), 1851-1917. Boston, Ginn
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