Lectures on the physiology of plants . e where they grow. In this they differ fr(nn all plagiotropic 704 LECTURE XL. organs, lateral rootlets, side shoots, and leaves, which under the influence of the sameexternal forces assume directions oblique to the horizon or even horizontal positions,and at the same time strive to present their flat surfaces at right angles to thestrongest light. True to the fundamental principle which we have throughout adopted, that whenorgans react differently towards the same external influences, this must necessarilybe caused by a difference in their organisation, w
Lectures on the physiology of plants . e where they grow. In this they differ fr(nn all plagiotropic 704 LECTURE XL. organs, lateral rootlets, side shoots, and leaves, which under the influence of the sameexternal forces assume directions oblique to the horizon or even horizontal positions,and at the same time strive to present their flat surfaces at right angles to thestrongest light. True to the fundamental principle which we have throughout adopted, that whenorgans react differently towards the same external influences, this must necessarilybe caused by a difference in their organisation, we now inquire in the first placewhether all orthotropic organs are distinct in their organisation from all plagiotropicones. It can be shown that in very many cases the relations of organisationare such as are indicated by the question; for all orthotropic organs are radiallyconstructed, and, on the other hand, all dorsiventral structures are it must be added that there are also many plagiotropic organs which. Fig. ?>ffj.—Phaseohis miillißorus, growing in damp soil behind a slieet of glass, k primary root; n lateral roots of the firstorder; n n lateral roots of the second order. The roughly horizontal line denotes the surface of the soil. as regards their coarser anatomy appear to possess radial structure, such as obliquelygrowing lateral roots and side-shoots which arise from orthotropic parent-organs;but we may assume in such cases that certain peculiarities of structure not yet known,and which are not necessarily visible by means of the microscope, determine theplagiotropism, and at the same time correlations of growth very often appear to co-operate also. For example, as has already been shown, the horizontal or obliquegrowth of the branches of a Fir, depends upon the presence of the orthotropic apexof the primary stem, and it may be added that a similar dependence exists alsobetween the primary and lateral roots of many plants. For example,
Size: 1838px × 1359px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, booksubjectplantph, bookyear1887
