. Plants; a text-book of botany. Botany. 36 PLANT RELATIONS. framework of veins is variously arranged. The large veins which enter the blade send off smaller branches, and these send ofE still smaller ones, until the smallest veinlets are invisible, and the framework is a close network of branching veins. This is i^lainly shown by a '"skel- eton " leaf, one which has been so treated that all the green sub- stance has disap- peared, and only the network of veins remains. It will be noticed that in some leaves the veins and veinlets are very prominent, in others only the main veins are
. Plants; a text-book of botany. Botany. 36 PLANT RELATIONS. framework of veins is variously arranged. The large veins which enter the blade send off smaller branches, and these send ofE still smaller ones, until the smallest veinlets are invisible, and the framework is a close network of branching veins. This is i^lainly shown by a '"skel- eton " leaf, one which has been so treated that all the green sub- stance has disap- peared, and only the network of veins remains. It will be noticed that in some leaves the veins and veinlets are very prominent, in others only the main veins are jM'ominent, while in some it is hard to detect any veins (see Figs. 25, 26). :1'J. Significance of leaf veins.—It is clear that the framework of veins is doing at least two things for the blade: (1) it mechanicuUy supports the spread out green sub- stance ; and (2) it conducts material to and from the green substance. S(j complete is the network of veins that this. Fig. 26. A leaf of hawthorn, showing a short petiole, and a broad toothed hlade with a conspicuons network of veins. Note the relation between the veins and the teeth.—After Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Coulter, John Merle, 1851-1928. New York, D. Appleton and company
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