. Un manuel de botanique pour les collèges et universités ... La botanique. 931 Début de germination la germination des graines dans le fruit (comme dans le citron). La cause de la viviparité est inconnu, bien que si la formation des graines de plus en plus de résultats le xérophytisme ou de nutrition- décroissant, la viviparité est peut-être dû à la poursuite de conditions favorables au développement---vege ou à la création de telles conditions à la maturité des fruits. Cette idée semble être favorisée par le fait que diverses graminées pièce viviparité en automnes humides, et que les pois et les haricots, lors de conditions de végétation sont favorables, souvent pièce u

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. A textbook of botany for colleges and universities ... Botany. GERMINATION 931 early germination of seeds within the fruit (as in the lemon). The cause of vivipary is unknown, though if seed formation results from increasing xerophytism or from decreas- ing nutrition, vivipary may be due to the continuance of conditions favorable to vege- tative development or to the inception of such conditions at fruit maturity. This idea seems to be favored by the fact that various grasses exhibit vivipary in wet autumns, and that peas and beans, when vegetative con- ditions are favorable, often exhibit uninter- rupted embryo development. Approaching such vivipary is the germination of seeds while still within the fallen fruits of Typha and A ndropogon. Seed maturity and germination. — A number of seeds are capable of germi- nation as soon as they are shed; among such are those of the willows, the sen- sitive plant, and many cycads, crucifers, and grasses.' It is a matter of com- mon belief, however, that most seeds require a resting period of some weeks or months before they are capable of germination, and that in temperate and in cold climates germination ensues only after a period of rest in the ground, coupled with exposure to low temperatures. In many seeds under ordinary conditions the germinative capacity may improve with age, a cer- tain percentage being capable of germi- nating after the first winter, a larger percentage after the second winter, and in a few instances a still larger percent- age after the third winter; it is said that the seeds of certain conifers are ^ It will be recalled that willow seeds soon lose their vitality, especially if desiccated; seeds of the sensitive plant, however, have been known to retain their vitality for sixty years.. Figs. 1225-1227. — Vivipary in the mangrove (Rhizophora Mangle): 1225, a mature fruit attached to the tree, the basal portion of the embryo (r) just emerging; 1226, a later stage in which the young plant has become

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