. Botanique de la plante vivante. Botanique ; les plantes. Fig. 127. Deux sections de tiges de Carex. Un rhizome, de Carex arenaria avec tissu mécanique dans le condensé, aussi résistant à la corde-exigence. ( X 14.) B, Carex vulgaris, tiges aériennes construites de manière à répondre aux besoins en colonnes. ( X 25.) plus clairement dans le sable, de carex où le cortex est très faible et, bien que les caissons stèle est compacte cimentées ensemble avec sclérotiques, de manière à former un noyau solide (Fig. 127, A). C'est un con- contraste à la tiges aériennes de la plupart des carex (Fig. 127, B). Support tiges pendantes, lourde- ment les fruits

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. Botany of the living plant. Botany; Plants. Fig. 127. Sections of stems of two Sedges. A, Rhizome of Carex arenaria with mechanical tissue condensed centrally, as resistant to the rope-requirement. ( x 14.) B, Carex vulgaris, aerial stem constructed to meet the columnar requirement. ( x 25.) more clearly in the Sand Sedge, where the cortex is very weak and lacunar, while the stele is compactly cemented together with sclerotic tissue, so as to form a solid core (Fig. 127, A). This is in sharp con- trast to the aerial stems of most Sedges (Fig. 127, B). Stems support- ing heavy, pendent fruits show a like structure ; also submerged and some climbing stems, all of which are liable to longitudinal tension. The similar modification of plants of such various habit, when subjected to the same mechanical demand, indicates that the rope-like concentration is adaptive. The problem for strut-roots, such as are seen at the base of the stem of the Maize, is a mixed one ; for the roots on the windward side of the plant suffer longitudinal tension, while those on the lee side act as oblique struts, and are subject to columnar pressure. The structural requirements are thus opposed. The mechanical tissues in such roots are found to form two systems (Fig. 128). The stele is compact, and cemented together in a hollow ring, which is, however, wider than in the underground roots. It is suited to resist longitudinal tension, but is not highly specialised to meet it. The cortex is, however, sclerotic, the thickening being greatest at the periphery. This is suited to meet the columnar. 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.. Bower, F. O. (Frederick Orpen), 1855-1948; Wardlaw, C. W. (Claude Wilson), 1901-. London, Macmillan and Co. , ltd.

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