Text-book of structural and physiological botany . examination. When they are notso adapted, they must be dissected into small trans-parent pieces; and the direction in which thesection has been made must also be noted. Inorder to examine, for example, the structure of abranch, preparations must be made, taken from itprincipally in the following three ways (Fig. 96) :in the transverse section a b 2X right angles to theaxis of growth mn, the longitttdinal section cdthrough the axis, and the tangential section efparallel to it. Sections in other directions, as theoblique gh, are only occasionall
Text-book of structural and physiological botany . examination. When they are notso adapted, they must be dissected into small trans-parent pieces; and the direction in which thesection has been made must also be noted. Inorder to examine, for example, the structure of abranch, preparations must be made, taken from itprincipally in the following three ways (Fig. 96) :in the transverse section a b 2X right angles to theaxis of growth mn, the longitttdinal section cdthrough the axis, and the tangential section efparallel to it. Sections in other directions, as theoblique gh, are only occasionally needed. Incertain cases it is also requisite, in order to makethe preparation transparent or decompose it intoits separate elements, to macerate it, especiallywhen it is desired to determine the form and con-nection of the individual cells. We have here nospace to enter into a detailed account of the ap-plication of the microscope to botanical investiga-tion, and can only refer to theworks of Dippel,Harting, Nageli and Schwendener, and Fig. 96,—Diagram re-presenting the varioussections of a stem. CHAPTER IV. THE EXTERNAL FORM OF PLANTS. In the plants of lowest organisation, Algse, Fungi, andLichens, the contrast which is so manifest in those morehighly developed between an axis (stem and root) and thelateral organs (leaves), is altogether wanting. With referenceto this point, the vegetable kingdom is therefore dividedprimarily into plants without an axis or Thallophytes^ andplants with an axis or Connophytes^ the term thalbis beingapplied to a structure destitute of leaves. The external differentiation of the parts in cormo-phytes can be very well seen in a germinating pea. If the 70 Structural and Physiological Botany. leathery skin [or testa] is stripped from a pea which hasbeen soaked in water, two large fleshy masses are seen, thecotyledons^ enclosing a small cylindrical body, the axis (, 98), which bears two minute leaves at its extremity ;the cotyledo
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