Organography of plants, especially of the archegoniatae and spermaphyta . n, which as we shall see is widely spread elsewhere, is connectedwith the fact that the leaf-apices have first to serve as protection to the bud,because they reach furthest outwards, and we have seen in the Musci thatthe leaf-tips in plants inhabiting dry places arc prolonged into diaphanous X 2 3o8 LEAF-DEVELOPMENT IN PTERIDOPHYTA AND SPERMOPHYTA hair-points, which form a little tuft above the stem-bud. The growingportions are, however, covered over and protected within the bud. Forerunner-tips, This precedence of the l
Organography of plants, especially of the archegoniatae and spermaphyta . n, which as we shall see is widely spread elsewhere, is connectedwith the fact that the leaf-apices have first to serve as protection to the bud,because they reach furthest outwards, and we have seen in the Musci thatthe leaf-tips in plants inhabiting dry places arc prolonged into diaphanous X 2 3o8 LEAF-DEVELOPMENT IN PTERIDOPHYTA AND SPERMOPHYTA hair-points, which form a little tuft above the stem-bud. The growingportions are, however, covered over and protected within the bud. Forerunner-tips, This precedence of the leaf-apex appears speciallyprominent in a number of climbing plants, and Raciborski ^ has recentlyshown the biological significance of it to them. It lightens at first theweight of the shoot, which is in search of a support in its revolving nutation,and consequently makes possible a much stronger growth in length of thisshoot out of an equal amount of available material. Raciborski designatesthe early developed apical portion of the leaf \.\\q forerunner-tip (Figs. 199,. Fig. 201. Benincasa cerifera. I, young leaf: the orerunner-tip, F, precedes markedly the development of thelamina. II, mature leaf: the distinction of the forerunner-tip hardly visible. Ill, branched tendril in juvenilestate: no vegetative point of a shoot is visible between the two tendrils, even at the apex of the larger tendrilthe tissue is still embr3onal ; g/, vascular bundle. I, magnified 9. II, natural size. 2CO, V). On the young leaf (Fig. 200, III) the forerunner-tip is essen-tially complete in development, and is almost twice as long as the primor-dium of the leaf-lamina L, which is still very small, but this, as a comparisonwith the older leaves shows, grows afterwards, whilst the forerunner-tipexhibits only an insignificant elongation at its base. The leaf-apex ina compound leaf shows the same features. In Fig. 201, which illustratesthe development of the leaf in Benincasa cerifera the precedence in
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