Lectures on the physiology of plants . otropism, and in others again the so-calledhydrotropism co-operates. I will give one or two examples of each of these cases. I demonstrated in 1874 that the lateral roots which originate from primary rootsassume their oblique direction solely under the influence of geotropism, and thiswas the first case of geotropism of this kind which was known at all. SupposeFig. 400 to represent the upper part of the primary root of a seedling of Vicia Faha,which has been grown behind a pane of glass in a box filled with loose soil, andhas developed numerous lateral ro
Lectures on the physiology of plants . otropism, and in others again the so-calledhydrotropism co-operates. I will give one or two examples of each of these cases. I demonstrated in 1874 that the lateral roots which originate from primary rootsassume their oblique direction solely under the influence of geotropism, and thiswas the first case of geotropism of this kind which was known at all. SupposeFig. 400 to represent the upper part of the primary root of a seedling of Vicia Faha,which has been grown behind a pane of glass in a box filled with loose soil, andhas developed numerous lateral roots, which have grown straight out laterally anddownwards at oblique angles with respect to the horizon. At that time it wasdoubtful whether the latter happened in consequence of a geotropic cftect-; thequestion therefore was, whether lateral roots are geotropic at all. By meansof the apparatus represented in Fig. 384, p. 682, I con\-inced myself in thefirst place that the lateral roots are verv cli-arly affected by centrifugal FIG. 399.—.4 a fructification (Apo-thecium) a of the Lichen Peltigiracanina on the rolled up supportinfrportion r r, which springs from theflat vegetative body t. B transversesection of A. 7oS LECTURE XL. cur\-ing away from the centre of rotation, which removes all doubt as to theirgeotropism. When I reversed the box, in which the seedling just referred to was grow-ing, so that the apex of the primary root was turned upwards, the tip of theroot curved vertically downwards; the direction of growth of the lateral rootletschanged also, their apices likewise curving downwards not vertically, but onlyobliquely, and this so that they grew on at about the same angle with respect to thehorizon as before the reversal of the box. Those portions of the lateral rootletswhich are quite black in the figure are the portions which were growing during theinverted position. The box was then placed upright again, and the lateral rootsonce more curved obliquely do
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectplantph, bookyear1887
