. Un cours pratique de botanique, avec une référence particulière à ses roulements sur l'agriculture, de l'économie, et de l'assainissement. La botanique. 26 Cours pratique en botanique anchorage et laissé à la dérive sur la terre. La propagation- ing, buissonnante tops deviennent très léger après la fructification, de manière à être aisément soufflée par le vent, laissant tomber leurs graines comme ils vont, jusqu'à ce qu'ils finalement est prise dans les fossés et les coins de clôture, où ils s'accumulent souvent en grand nombre au cours de l'automne et l'hiver. 24. Les avantages de la dispersion. - Des semences ne peuvent germer que si elles sont placées dans un endroit approprié sur le sol, l'moistur

• Contributeur: The Book Worm / Alamy Banque D'Images
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. A practical course in botany, with especial reference to its bearings on agriculture, economics, and sanitation. Botany. 26 PRACTICAL COURSE IN BOTANY anchorage and left to drift about on the ground. The spread- ing, bushy tops become very light after fruiting, so as to be easily blown about by the wind, dropping their seeds as they go, until they finally get stranded in ditches and fence corners, where they often accumulate in great numbers during the autumn and winter. 24. The advantages of dispersal. — Seed cannot germinate unless they are placed in a suitable location as to soil, moisture, and temperature. In order to increase the chances of secur- ing these conditions, it is clearly to the advantage of a species that its seeds should be dispersed as widely as possible, both that the seedlings may have plenty of room, and that they may not have to draw their nourishment from soil already exhausted by their parents. The farmer recognizes this principle in the rotation of crops, because he knows that successive growths of the same plant will soon exhaust the soil of the substances re- quired for its nutrition, while they may leave it richer in nourishment for a different crop. 25. Self-planting seeds.— Dispersal is not the only problem the seed has to meet. The majority of seeds cannot germinate well on top of the ground, and must depend on various agencies for getting under the soil. Some of them do this for themselves. The seeds of the stork's-bill, popularly known as "filarees, " have a sharp-pointed base and an auger-shaped appendage at the apex, ending in a projecting arm (the " clock" of the filaree) by which it is blown about by the wind with a whirling motion. Fig. 45. — Self-planting pod of peanut.. 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.. Andrews, Eli

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