. Eine Einführung in die pflanzlichen Physiologie. Pflanzenphysiologie. 354 pflanzlichen Physiologie Dieses rhythmische Änderung im protoplasma ist nicht durch Organe während des Wachstums nur ausgestellt; in vielen Fällen ein Leben lang bestehen bleibt. Sehr auffällige Instanzen werden durch bestimmte Bewegungen oft durch die Blätter der besonderen Pflanzen ausgestellt. Vielleicht die meisten dieser vertraut ist die so genannte Telegraph Pflanze, Desmodium gyrans oder Hedysarum. Die Blätter sind Ternate, der endfieder sehr im Vergleich mit den beiden seitlichen (Abb. groß. 151). Wenn die Anlage sah während ausgesetzt Suita

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. An introduction to vegetable physiology. Plant physiology. 354 VEGETABLE PHYSIOLOGY This rhythmic change in the protoplasm is not exhibited by organs during growth only; in many cases it persists throughout their life. Very conspicuous instances of it are afforded by certain movements often exhibited by the leaves of particular plants. Perhaps the most familiar of these is the so-called Telegraph plant, Desmodium or Hedysarum gyrans. Its leaves are ternate, the terminal leaflet being very large in comparison with the two lateral ones (fig. 151). If the plant is watched while exposed to suitable tempera- ture and illumination, the lateral leaflets are found to move up and down on the rachis, sometimes passing through an angle of 180°, and twisting slightly as they move. They thus describe a kind of ellipse, the duration of the movement being about two minutes. Many other instances of a similar kind are known, the Legum.inosce furnishing many ex- amples. All of them do not exhibit the movements with the same ease, as they are interfered with by other changes in position which Fig. 151—Tbbnate leaf op result from external stimulation. («-T™rm They can often be made evident by keeping the plant under constant external conditions. Darkness, however, if too prolonged causes their cessation, though in some cases they are made evident by deprivation of light for a short time. The mechanism of the movement in most of these cases is the rhythmically varying turgescence of particular organs known as pulvini, which are situated at the bases of the stalks of the leaves or leaflets. As in the cases already noticed, the, alternations in the turgescence are the expres- sion of rhythmic changes in the protoplasm of the cells of each pulvinus. As these pulvini play a considerable part in the changes of position which are exhibited by many leaves under various conditions, their structure may well attract. Please note that these images are extracted from scanned page images that

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