Text-book of botany, morphological and physiological . ^hich correspond to darkness on the one handand to daylight on the other hand pass over only gradually into one another. Light ^ Sachs, Arbeit, des bot. Inst. Wiirzburg, 1872, p. 168 et seq. The plants observed werechiefly Fritillaria imperialis, Humulus Lupulus, Dahlia variabilis, Polemonium reptatis, and Richardiaccthiopica. 746 . MECHANICAL LAWS OF GROWTH. requires a considerable time in order to overcome the nocturnal, darkness a con-siderable time to overcome the diurnal condition of the plant. If this were not thecase, the curve of g
Text-book of botany, morphological and physiological . ^hich correspond to darkness on the one handand to daylight on the other hand pass over only gradually into one another. Light ^ Sachs, Arbeit, des bot. Inst. Wiirzburg, 1872, p. 168 et seq. The plants observed werechiefly Fritillaria imperialis, Humulus Lupulus, Dahlia variabilis, Polemonium reptatis, and Richardiaccthiopica. 746 . MECHANICAL LAWS OF GROWTH. requires a considerable time in order to overcome the nocturnal, darkness a con-siderable time to overcome the diurnal condition of the plant. If this were not thecase, the curve of growth would at once rise abruptly in the evening when the roomis suddenly darkened, would then continue at the same elevation till morning, fallabruptly when light is again let in, and continue at the same height till the this does not correspond to the observed phenomena. In order to study more closely the changes of growth occasioned by internal causes,or the dependence of these changes on external conditions, it is necessary to measure. Fig. 450.—Arc-indicator, or apparatus for measuring the development of an internode of a growingplant a during short periods of time. the increments in short spaces of time such as an hour or two or three hours. In thecase of internodes or leaves of large plants which are growing very rapidly, as the flower-stems of Agave or the leaves of Musaceae, this can be done with a certain degree ofexactness by simple measurement with a measuring-rod. But for the purpose of moreexact observations it is more convenient to make use of smaller plants which do notgrow so rapidly, the growth during an hour not amounting to more than a millimetre, oreven less. In such cases a simple measuring-rod is not sufficiently exact; and I haveemployed in its place three different methods. In each of them a thin but strong threadof silk is fixed to the upper end of the stem or internode of the plant growing in apot, the thread passing vertically over an e
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectbotany, bookyear1875
