A contribution to our knowledge of seedlings / by the Right Hon. Sir John Lubbock.

  • John Lubbock, 1st Baron Avebury
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: A contribution to our knowledge of seedlings / by the Right Hon. Sir John Lubbock. Source: Wellcome Collection.

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    Tlie cordate form, then, appears to be the early, the palmate a later form. But how has the palmate form arisen ? The origin is perhaps connected with the manner in which the leaves are folded up, more or less like a fan, into the bud, so as to save space. Another advantage perhaps is that in cordate leaves with veins following the curvature of the leaf—as, for Fig. 1.—Loaf of Tamus, to show the curved course of the veins. Fig. 2.—Leaf of Sycamore (Acer), to show the straight course of the veins instance, in Tamus (fig. 1)—the vascular bundles pursue necessarily a curved course ; while in palmate leaves, as in Acer (fig. 2), the veins are straight; and it is clearly an advantage that the main channels which convey the nutritive fluid should hold a direct course. In such cases the leaf naturally assumes the lobed form with the vein running to the point of each lobe. There has indeed been some question whether the path of the sap lies mainly in the cell-walls or in the cell-cavities; but
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