The microscope : and its application to vegetable anatomy and physiology / by Dr. Hermann Schacht ; edited by Frederick Currey, M. A.

  • Hermann Schacht
Date:
1855
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Licence: Public Domain Mark

Credit: The microscope : and its application to vegetable anatomy and physiology / by Dr. Hermann Schacht ; edited by Frederick Currey, M. A. Source: Wellcome Collection.

    161/230 (page 137)
    It is, therefore, incorrect to suppose that the stem is formed out of leaves grown together; the nature of its develoiJement shows directly the contrary. In the dicotyledonous embryo the simple central portion—that is, the axis—a})pears fiist; the two cotyledons proceed from it on either side, and between the coty- ledons lies the plumule, which answers to the Puuctum vegeta- tionis of the apex of the stem. The first two leaves, therefore, are formed to a certain extent out of the stem by the division of it, and not the stem by the growing together of two leaves. The further progress of developement corroborates this. At the points where new leaves originate there is formed contem- poraneously with them a side branch of a vascular bundle of the stem, the gro^vth of which progresses equally with, and in the same manner as, the growth of the leaf. The leaf, there- fore, receives its vascular bundles from the stem, but a new vascular bundle never originates in the leaf to unite with the vascular bundles of the stem, The same rule holds with respect to the origin of new buds in the axils of the leaves ; and witli respect to the cambium-ring of the stem and of the root. The first rudiments of new buds, as well as of side-roots, always originate out of the vascidar bundle of the stem. The only places where the formation of much new substance for the buds and leaves takes place, are, the apex of the axis, and the cambium of the vascular bundles of the stem. I have dwelt longer upon this part of the subject, because the point, which is one of much importance, has by no means re- ceived the attention it deserves, and but few well-grounded ob- sei'vations have been made upon the subject. It is of the greatest importance that very accurate sections alone shoidd be used; oblique sections have been the cause of much error. The best way of guarding against this error is, to make the finest ]x>s- sible longitudinal sections through the apex of the stem, to })lace them together under the microscope, and to select those sections which appeal’ to be cut quite perpendicularly thi’ough the stem, as well as exactly through its middle. When such a section is properly made, the Punctum vegetationis always ap- pears in the form of a small cone; if this is not the case the section is either not cut perpendicularly through the stem, or X 3