. Le cytoplasme de la cellule végétale. Les cellules et les tissus des végétaux ; le protoplasme. Chapitre VI - 45 - Les plastes les chloroplastes dans les plantes vasculaires : théorie de Schimper :- dans les plantes vasculaires, ptéridophytes et phanérogames marines, comme cela a été dit, n'est pas la chlorophylle présente dans les cellules embryonnaires et est formé uniquement d'organes exposés à la lumière comme les cellules des organes de distinction. Les chloroplastes sont donc trouvés seulement dans les tissus verts. La question de l'origine des chloroplastes est resté longtemps sans solution. Les anciens botanistes a conclu que ces corps ont été formés par entiation- diffèrent du cytoplasme ou t

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. The cytoplasm of the plant cell. Plant cells and tissues; Protoplasm. Chapter VI — 45 — The Plastids The chloroplasts in vascular plants: theory of Schimper:- In vascular plants, pteridophytes and phanerogams, as has been said, chlorophyll is not present in embryonic cells and is formed only in organs exposed to light as the cells of the organs differentiate. Chloroplasts are therefore found only in green tissue. The question as to the origin of chloroplasts remained a long time unsolved. The older botanists concluded that these bodies were formed by differ- entiation from the cytoplasm or that they were the result of the transformation of starch grains. Schimper (1881-1885) showed for the first time that the chloroplasts are derived in reality from small colorless bodies, protein in nature, which are found in all the colorless tissues of plants. To these bodies he gave the name leucoplastids. These were later called trophoplasts (Meyer) and leucoleucites (VAN TiEGHEM). We shall call them leucoplasts^. These are very small, rounded, or rod-shaped elements which are found scattered in great numbers in the cytoplasm and which are transmitted from cell to cell by division. All these leucoplasts have the ability to form starch grains, i.e., to con- dense in the form of starch, the hexoses elaborated in green tis- sue during photosynthesis and later transported to colorless tissues (roots, tubercles, etc.). Whenever the hexoses accumu- late in green tissues in too high concentrations, the leucoplasts become amyloplasts. One of the classic examples of this formation of starch through the agency of the leuco- plasts is to be found in the root of Phajus grandifolius in which Schimper succeeded in following the entire process. In this root, the leucoplasts are indeed rather large, rod- or spindle-shaped, bodies enclosing each along its axis a needle-shaped crystalloid cf protein, the product of its elaboration. The starch grain arises in a peripheral region of the thic

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