. La botanica della pianta vivente. La botanica. Costruzione meccanica della pianta-corpo 143 rigidità come sulla base di specifici tessuti meccanici. Tali metodi servono a conferire la necessaria resistenza meccanica al giovane parti. Ma come i tessuti crescono, le loro pareti diventano dense- ulteriormente rafforzata. Essi sono quindi meno suscettibile di turgore, e sono anche più resistenti alla crescita. Inoltre, nei vecchi pezzi meccanici di richiesta di supporto aumenta con il crescente onere di foglie e rami. Queste richieste vengono soddisfatte dai meccanici specifici tessuti, equipaggiato con le loro pareti ispessita per offrire una maggiore resistenza. Se

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. Botany of the living plant. Botany. MECHANICAL CONSTRUCTION OF PLANT-BODY 143 Rigidity as based on Specific Mechanical Tissues. Such methods serve to give the necessary mechanical strength to young parts. But as the tissues grow older, their walls become thick- ened. They are then less susceptible to turgor, as they are also more resistant to growth. Moreover, in the older parts the mechanical demand for support increases with the increasing burden of leaves and branches. These demands are met by specific mechanical tissues, fitted by their thickened walls to offer greater resistance. Though the effect of turgor is characteristic of young plants, and that of the specific mechanical tissues of the mature, there is no definite limit. Fig, 102. Collcnchyma from stem of the Potato, seen in transverse section, ( x 300.) between the action of each. The dependence on the one merges gradually with age into dependence on the other, and in the growing part both sources of support may be effective at the same time. There are two types of specific mechanical tissue, [a) CoUenchyma, which is found in growing herbaceous stems and leaves ; and {b) Scleren- chyma, which is characteristic of more mature parts. CoUenchyma consists of cells which retain their living protoplasts, and thus remain physiologically active, while chlorophyll corpuscles are frequent in its cells. These cells usually have the form of 4-6-sided prisms, with transverse or oblique ends, and are sometimes transversely partitioned. The cell-walls are composed of cellulose, which is swollen in life with water. They are thicker at the angles of the prisms than at their flattened sides, where the thinner membrane allows of ready physio- logical interchange. This gives the tissue, when seen in transverse section, the appearance shown in Fig. 102. It is thus a tissue which, . Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appe

Parole chiave associate all'immagine

• bookcentury1900
• bookdecade1910
• booksubjectbotany
• bookyear1919