. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. 332 THE SEED-HABIT As regards the former feature, the only essential difference from Selaginella lies in the germination of the microspores in close proximity to the megaspore, for which special devices such as the mucilaginous poUination drop and the pollen chamber are created. Moreover, with the help of the pollen tube some nourish- ment is obtained from the adjacent nucellus. The seed may be looked upon as an extreme development of heterospory. Even in Selaginella it was noted that in some species there ma
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. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. 332 THE SEED-HABIT As regards the former feature, the only essential difference from Selaginella lies in the germination of the microspores in close proximity to the megaspore, for which special devices such as the mucilaginous poUination drop and the pollen chamber are created. Moreover, with the help of the pollen tube some nourish- ment is obtained from the adjacent nucellus. The seed may be looked upon as an extreme development of heterospory. Even in Selaginella it was noted that in some species there may be reduction to a single megaspore, which is retained within the sporangium till after fertilisation (cf. p. 319).. Fig. 191A.—Restoration of the seed (Lagenostoma lomaxi) of Lyginopteris oldhamia, in its glandular cupula. (After Oliver.) Such reduction and retention are eminently characteristic of the seed-habit, where dehiscence of the megasporangium is dispensed with. The added protection, furnished by the integument, admits of a change in the character of the sporangium-wall, which becomes a thin-walled tissue ser-ing as intermediary between the -ascular sj'stem of the ovule and the developing megaspore and female prothallus. The possession of a vascular system, another characteristic of the ovule, facilitates nutrition and the storing up of food- reserves for the young embryo. It is probably in consequence of the increased food-supply that o'ules and seeds in general attain so large a size as compared with the sporangia of lower. 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 work.. Fritsch, Felix Eugene, 1879-; Salisbury, E. J. (Edward James), Sir, b. 1886. London, G. Bell and sons ltd.