. La botanique pour les lycées et collèges. La botanique. 54 BOTANT. stances dans certaines usines et uniformément dans d'autres) deux ou plusieurs noyaux se produisent dans chaque grain ; par la croissance des grains tels devenir enceinte et peut enfin se séparer en autant de parties qu'il y a des noyaux. 69.- âThe structure moléculaire du grain d'amidon a été déterminé à être semblable à celui de plante-cellulose. C'est re- considérée comme composée de molécules, dont chacune est entourée d'une couche aqueuse de plus ou moins d'épaisseur. La croissance se fait par l'intercalation de molécules nouvelles entre le pré- viously onesâin ont formé d'autres termes, par intuss

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. Botany for high schools and colleges. Botany. 54 BOTANT. tionally in some plants and uniformly in others) two or more nuclei occur in each grain ; by growth such grains become compound and may finally separate into as many parts as there are nuclei. 69.âThe molecular structure of the starch grain has been determined to be similar to that of plant-cellulose. It is re- garded as composed of molecules, each of which is surrounded by a watery layer of greater or less thickness. Growth takes place by the intercalation of new molecules between the pre- viously formed onesâin other words, by intussusception, exactly as in the case of ^ the cell-wall. During ihe formation of the grain, in L C77/@ certain portions of it the IkWp® watery layers surrounding the molecules become thicker. When seen by transmitted light such more watery parts appear darker than those which are less watery, and an ex- >|© amination shows that they surround the nucleus on all sides in a concentric manner. In this way -the starch grain comes to be made up of alternating layers of more and less watery substai:ee. Every watery layer is thus between two layers which contain less water, and so every less watery one lies between two more watery ones. As an increase in the amount of water in any portion of the starch grain de- creases the density of that portion, the layers just described may be distinguished as of greater density when having less water and of less density when having more water.. Kg. 44, . , , (Fiffum sativum). St, starch grains with nucleus and concentric striie ; a, granules of aleurone ; i, 2, intercellular spaces. X 800.âAfter Sachs. -Cella from the cotyledon of the pei " " â iclei: should be abandoned, as it was originally given under the mistaken notion that it was the point of attachment of the starch grain, while growing.. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration

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