A students' text-book of botany / by Sydney H. Vines.

Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: A students' text-book of botany / by Sydney H. Vines. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    y. Proteid Grains, or Aleuron, are granules of various sizes, oval or spherical in form, which occur in seeds, and are of physiological importance in that they are the source from which the embryo is supplied with nitrogenous food when the seed germinates. They consist of a mixture of proteid substances belonging to the globu- lins and the albumoses. They present no indications of structure, and are much larger in oily than in starchy seeds. The proteid grain always contains a mass of mineral matter. Most commonly this is a rounded body, the globoid (-Fig. 68), con- sisting of double phosphate of lime and magnesia ; less frequently there is a crystal, or a cluster of crystals, of calcium oxalate. In the large grains of oily seeds it is frequently the case that a portion of the of the grain crystal- lises out, constituting the crystalloid ; there are occasionally two or more crystalloids in the grain (Fig. 68). The grains are seci’eted in vacuoles of the cyto- plasm which, when the grains have been dis- solved out, remains as a Proteid crystalloids are also occasionally found, independently of aleuron, in the cells of plants, (e.g. tuber of the Potato ; epidermal cells of leaf of Poly- podium irroides ; some Rhodophyceas). The crystalloids (whether free or in proteid grains) differ from ordinary mineral crystals in that, when treated with various reagents, they absorb liquid and swell up. They are for the most part cubical, tetrahedral, or rhomboidal in form. 8. Mineral Crystals are frequently found in the cells of plants. They sometimes consist, but in comparatively few cases, of calcium carbonate; for example, the crystals in the protoplasm of Myxo- mycetes, and the crystalline masses occurring in the cells of the network (Fig. 68 D). proteid (globulin) Fig. 70.—Part of a section of a grain of wheat Triticum vulgare : p pericarp; t seed-coat or testa; internal to which are cells belonging to the endo- sperm ; the external layer contains small proteid- grains (ul) but no starch, the more internal cells con- tain starch-grains am; n the nucleus. (After Stras- burger: x 240.)