. The cytoplasm of the plant cell. Plant cells and tissues; Protoplasm. Chapter VI â 49 â The Plastids and that these granules present the histochemical characteris- tics of lipides and not those of aldehydes (Cf. p. 209). Just what these granules signify is still very obscure. In cells in which the plastids never form starch, the granules are often considered as assimilation products replacing starch. It has been noticed, sometimes, that these granules appear in large numbers during the period preceding the formation of starch and of chlorophyll and carotinoid pigments, only to disappear as s
. The cytoplasm of the plant cell. Plant cells and tissues; Protoplasm. Chapter VI â 49 â The Plastids and that these granules present the histochemical characteris- tics of lipides and not those of aldehydes (Cf. p. 209). Just what these granules signify is still very obscure. In cells in which the plastids never form starch, the granules are often considered as assimilation products replacing starch. It has been noticed, sometimes, that these granules appear in large numbers during the period preceding the formation of starch and of chlorophyll and carotinoid pigments, only to disappear as soon as these products have been formed. It was therefore thought that they might be an intermediate product contributing to the formation of starch or pigment. It has also been shown that very frequently similar granules appear in great numbers in plas- tids as they degenerate in the cells of flowers which are beginning to take form. In this case, the presence of the granules can only be explained as a breaking down of the plas- tidial lipoprotein complex, , as a process called lipophanerosis (demasking of lipides. Cf. p. 203, 205). Finally, large globules have recently been de- scribed in the plastids of various Cactaceae (Cephalocereus, Echinocereus, etc.). They pre- sent the histochemical characteristics of phyto- sterol and form in the plastid exactly as do starch grains. These globules always precede starch formation and disappear the moment that starch appears. It was therefore supposed by ^J^^;i[^n7 ^Sfof those who did the work that these globules of â¢^ Veig'^a^ith lip- phytosterol constituted a material which served '^^ granules in the . "^ , â, 1 ,r^ â »«â¢â¢ chloroplasts. m the buildmg up of starch (Savelli, Miss Manuel) (Fig. 19). For a very long time it was impossible to obtain paraffin sec- tions of preserved and stained plastids, at least of leucoplasts, for they were destroyed by all fixatives then used, and only the much more resistant
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