Image d'archive à partir de la page 116 du cytoplasme de l'usine. Le cytoplasme de la cellule végétale cytoplasmofplant00guil Année : 1941 Chapitre X - 101 - Dualité de l'Ghondriome cellules qui nous avons étudié et l'chondriosomes de Saprolegnia montrent exactement la même réfringence. Légèrement supérieure à celle du cytoplasme, ce, bien que de réfractivité très légère, permet encore l'chondriosomes d'être bien vu. En vertu de l'ultramicroscope les deux catégories d'éléments de cellules épidermiques et le chondrio- somes de Saprolegnia se distinguent seulement dans des conditions très favorables. Lorsqu'elles sont visibles, ils

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Archive image from page 116 of The cytoplasm of the plant. The cytoplasm of the plant cell cytoplasmofplant00guil Year: 1941 Chapter X — 101 — Duality of the Ghondriome cells which we have studied and the chondriosomes of Saprolegnia show exactly the same refractivity. Slightly superior to that of cytoplasm, this refractivity, although very slight, still permits the chondriosomes to be adequately seen. Under the ultramicroscope the two categories of elements of epidermal cells and the chondrio- somes of Saprolegnia are distinguishable only under very favorable conditions. When visible, they always have the same appearance and are seen only because of their very faintly luminous contours. With the Zeiss micropolychromar they are made to appear very clearly with a different color from that of the cytoplasm, green on a red background, for instance, or yellow on violet. Chondriosomes and plastids of epidermal cells, as well as the chondriosomes of Saprolegnia, behave like extremely delicate elements which the least change in osmotic equilibrium, or the least pressure on the cover glass of a prep- aration, suffices to change into vesicles (cavulation). In a hypertonic medium they keep changing shape as long as the cell is liv- ing but as soon as it dies, they become vesiculate (Fig. 67). We have already seen that in Saprolegnia the chondrioconts are moved about slowly by the cytoplasmic currents and that dur- ing these displacements they change shape, passing through the most varied forms. They are even able to branch by growing a kind of pseudopodium which afterwards is retracted. In epidermal cells of tulip in which cytoplasmic movements are very slow or do not exist, nothing of this sort is ob- served. In cells of Iris germanica and of Allium Cepa, however, which are very favor- able objects for study, we have observed for the plastids these same displacements and the same instability of form. (Figs. 68, 70, 150). During the movement from place to place the plas

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