Lectures on the physiology of plants . y bent till it cracked; this evi-dently depends upon the fact that thelower side as it vigorously elongates andcurves upwards compresses the tissue ofthe passive upper side, a process which isintensified by the latter in its turn losingwater, as can be concluded with certaintyfrom the very considerable shortening. Ofmy very numerous measurements in thisconnection, I will only quote one in illus-tration of what has been said. A node ofthe Maize, about 12 mm. thick, was 5 on all sides : after it had lain six daysin a horizontal position the upper si
Lectures on the physiology of plants . y bent till it cracked; this evi-dently depends upon the fact that thelower side as it vigorously elongates andcurves upwards compresses the tissue ofthe passive upper side, a process which isintensified by the latter in its turn losingwater, as can be concluded with certaintyfrom the very considerable shortening. Ofmy very numerous measurements in thisconnection, I will only quote one in illus-tration of what has been said. A node ofthe Maize, about 12 mm. thick, was 5 on all sides : after it had lain six daysin a horizontal position the upper side hadbecome shortened by 0-5 mm. (i. e. y^^th ofits original length), while the lower sidehad become elongated by 7*5 mm., 12-5 mm. In other cases, however, theshortening of the upper side was stillmore considerable, (e. g. from 4 mm. to3,) while the length of the under sideincreased from 5 mm. to 11. Microscopicexamination shows that the cells of theepidermis and of the i)arenchyma of the lower half of the node have elongated. Fig. 388.—Portion of a Scarlet Runneroriginally growing erect, has been for some hours turnedupside down to show the geotropic curvatures of themotile organs P, />,, Pi. MOTILE ORGANS OF LEAVES. 689 to an extent corresponding to the above numbers, l)ut without undergoing transversedivision. As in all similar cases of curvatures due to growth— even in the case oftendrils and, as we shall see later, of geotropically curved root-apices—the tissue ofthe side which has become convex consists of large cells, containing abundance ofwater and relatively little protoplasm; that of the concave side, like very youngtissue, of small cells with little water and much protoplasm. That the motile organs of periodically motile compound leaves can executegeotropic curvatures I first showed in 1865 in my Handbook/ employing the figurehere reproduced (Fig. 388): it represents a young Kidney Bean which together withits flower-pot was placed for about 4-6
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectplantph, bookyear1887
