. Anatomie végétale du point de vue du développement et les fonctions des tissus, et le manuel de micro-Technic. e les cellules mères apparemment indivis des tubes criblés de andcompanion cellules (voir page 37) ; puis ce sont laissés de côté, et theends des veines n'ont que des cellules de parenchyme de la frontière (qui aremorphologically une partie de le mésophylle ou fondamentale-paren chyma et non des faisceaux vasculaires), entourant le lasttracheids. Ces faits sont représentés de façon schématique inFig. 90. Les aliments de la palissade et du parenchyme spongieux dans le TRANSPORT D'ALIMENTS 164 forme d'carbohyhrate solubles tels

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. Plant anatomy from the standpoint of the development and functions of the tissues, and handbook of micro-technic. e apparently the undivided mother cells of sieve tubes andcompanion cells (see page 37); then these are left out, and theends of the veins have only border parenchyma cells (which aremorphologically a part of the mesophyll or fundamental paren-chyma and not of the vascular bundles), surrounding the lasttracheids. These facts are represented diagrammatically inFig. 90. The food from the palisade and spongy parenchyma in the 164 TRANSPORT OF FOODS form of soluble carbohyhrate such as grape sugar, or in sol-uble nitrogenous form such as asparagin and other amides, and even in the more complex form of soluble proteids, passesby diffusion into the border parenchyma cells of the smallestveinlets, and then begins its movement, still by diffusion andother ways about which we have no exact knowledge, towardthe larger veins which are to carry it out of the leaf or deliverit to the midrib for transportation. A very simple demonstra-tion shows that the food takes this course. After a day of active. FIG. 90.—Diagram indicating the succession of the conducting tissues of a vein fromthe base toward the apex, a, border parenchyma; b, companion cells; c, sieve tubes; d, undivided mother cells of companion cells and sieve tubes; e, tracheal elements. photosynthesis the leaves are loaded with starch at sundown.A leaf removed at this time, bleached in boiling alcohol, andstained with iodine, shows the blue starch reaction all over.By sunrise the next morning, however, a leaf when removed andtreated in the same manner takes on a yellowish color, showingthat the starch has disappeared. But if one of the principalveins is cut in the evening that portion of the leaf between thecut and the extremity of the vein, which of course would be thepart tributary to this vein, still retains its starch in the morning, while the rest of the leaf where the veins are left intact have beenem

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