. La fisiologia vegetale. La fisiologia vegetale. Il modo normale e possedeva normalmente difierentiated tessuti, ma il con- tinuously illuminato piante, sebbene essi contenevano più di clorofilla, pes- sessed una più semplice struttura anatomica rispetto agli altri e assomigliano in certi aspetti, piante cresciute in continuo le tenebre. Le foglie di Helk- horus niger, per esempio, aveva strutture normali quando le piante sono state oscurate ogni notte; il mesophyll com- decantata il solito strato di palizzata parenchima sopra (contenente la maggior parte dei cloroplasti) con allentato parenchima spugnoso sottostante, quest'ultimo avente nume

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. Plant physiology. Plant physiology. the normal way and possessed normally difierentiated tissues, but the con- tinuously illuminated plants, although they contained more chlorophyll, pes- sessed a much simpler anatomical structure than the others, and resembled in certain respects, plants grown in continuous darkness. The leaves of Helk- horus niger, for example, had normal structures when the plants were darkened every night; the mesophyll com- prised the usual layer of palisade parenchyma above (containing most of the chloroplasts) with loose spongy parenchyma below, the latter having numerous large air passages (Fig. 138, /). On the other hand, the Helleborus leaves grown with continuous illu- mination were very different from the others in several respects. Chloroplasts were here much more numerous than in the other case and they occurred almost through- out the entire tissue, instead of being mainly confined to the palisade. Instead of the loose, spongy parenchyma there was a tissue more like the fundamental parenchyma of growing regions, with almost no intercellular spaces at all (Fig. 138, F). , While photosynthesis is mainly dependent on the less refrangible half of the spectrum, normal growth and development require the more refrangible half (Fig. 132, curve XY). These more refrangible rays (blue and violet light) are strongly absorbed by plants. If, on a bright spring day, for example, the intensity of the blue-molet light is 666 in the open it is only 21 in the shade of a fir tree, all but about one thirty-second of the energy of these rays having been re- flected or absorbed by the leaves of the tree. Many formal characteristics of plants depend upon the intensity of the blue-violet light that reaches them. In evergreen plants, only the peripheral leaf-buds develop, since the interior buds are shaded, but in deciduous trees leaf-buds develop throughout the crown; in the latter case the tree is leafless at the time the buds are opening and all buds are

Parole chiave associate all'immagine

• bookcentury1900
• bookdecade1910
• booksubjectplantphysiology
• libro