. 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, or microsporophyll. 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- s
. 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, or microsporophyll. 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 Ibst all traces of a prothallium and is merely an antheridium which sooner or later produces two Fig. 218. Longitudinal Section generative cells. These are most through Fertilized Ovule of a easily seen in the pollen grain, ^P''"''®" but sometimes they are plainly i), pollen grains; «, pollen tubes; visible in the poUen tube (Fiff. n, neck of the archegonium; -inn t> . u, body of archegonium with i-^o, Jo J, nucleus; e, embryo sac filled Seed-plants are distinguished with endosperm. ^ ° from all other plants by their power of producing seeds, or enclosed megasporangia with embryos. 384. The Sexual Generation and Relationships of the Great Groups of Plants. — On summing up Sects. 381- 383 it is evident that the sexual generation in general. 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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