. De plus en plus ; le maïs, de juger, de reproduction, d'alimentation, le marketing ; pour l'agriculteur, étudiant et enseignant de l'agriculture, un manuel pour l'enseignement agricole et des shcools. Le maïs. STRUCTURK RACINE DE 41. Une section longitudinale à travers l'extrémité de la racine de la bourse-à-pasteur, montrant l'axe vasculaire central (pi), surj-ondé par le cortex (p), à l'extérieur de tne cor- tex l'épiderme (e) qui disparu les poires dans les parties les plus anciennes de la racine, et la racine de premier-cap (c). office de tourisme de ces cellules n'est qu'au gie la racine de la force et la forme, tandis qu'à travers eux et entre eux l'humidité absorbée par la couche extérieure rea

• Contributeur: The Book Worm / Alamy Banque D'Images
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. Corn; growing, judging, breeding, feeding, marketing; for the farmer, student and teacher of agriculture, a textbook for agricultural colleges and high shcools. Corn. STRUCTURK OF ROOT 41. A longitudinal section through the root tip of shepherd's purse, showing the central vascular axis (pi), surj-ounded by the cortex (p), outside of tne cor- tex the epidermis (e) which disap- pears in the older parts of the root, and the prominent root-cap (c). office of these cells is merely to gie the root strength and form, while through them and between them the moisture absorbed by the outer layer reaches the central cylinder within. The innermost layer of cells of the curtex _forms a very complete and very rigid cylinder, enclosing the central cylindi'r. This endodermh consists of regularly formed, closely- fitting cells which prevent the escape (if ])lant food on its course upward through the central cylinder of older roots. In younger plants, however, the passage of moisture from the surface to the cylinder is not hindered. The pericycle, though not very distinct in many roots, is the outer cell layer of the central cylinder. From single cells within it, arise all secondary roots. By pushing their way outward through the cortex and surface layer, and by repeated cell divisions they soon elongate and become tributary feeders. This internal origin of the branch roots can be readily seen by peeling off the cortex, which lays liare the attachment. The central cylinder consists for the most part of tubes which are of use in carrying the plant food upward into the stem and leaves. CONDITIONS AFFECTING ROOT GROWTH. The factors affecting root growth are the factors which affect the yield of the crop. (i) In order that the younger and more tender rootlets may push through the soil, its *structure must be quite fine. A root will not cross a large interspace between lumps of earth. (2) Corn roots draw almost entirely upon the capillary water of the soil. In case of extreme drought

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