416 STORAGE SYSTEM 



granular precipitate is thrown down in the cell-sap of the starch- 

 containing storage-cells ; by means of appropriate reagents this preci- 

 pitate may be shown to consist partly of amides (mainly in the form 

 of asparagin) and partly of native proteins. In ripe potatoes, a large 

 proportion (30-47 per cent.) of the total nitrogenous substance is 

 present in the form of " amide-nitrogen." If a section from a bulb- 

 scale of Allium Cepa is treated in the same way, only a slight flocculent 

 or semi-granular precipitate appears in the majority of the cells ; those 

 parenchymatous storage elements, however, which immediately adjoin 

 the leptome strands of the vascular bundles, become filled with a dense 

 precipitate, which probably consists in the main of protein substance. 

 The cells in question might in fact be regarded as members of a 

 " protein-sheath " [comparable to the more widely distributed " starch- 

 sheaths "]. The reserve amide-nitrogen of the Beet-root is principally 

 made up of glutamin, which is accompanied by a small amount of 

 betain. Generally speaking, a considerable proportion, and sometimes 

 the greater part, of the reserve nitrogen of succulent storage-organs 

 consists of soluble amides. 



In dry storage-organs, on the contrary, such as seeds and many 

 fruits, reserve proteins play so prominent a part, that non-albuminoid 

 substances, as a rule, only make up between 2 per cent, and 10 per 

 cent, of the total nitrogen. In these cases the protein-compounds 

 occur in special forms, which constitute a very characteristic feature of 

 quiescent storage-tissues. The most remarkable of these special forms 

 of reserve pxx)tein are the so-called crystalloids. 190 These bodies are 

 undoubtedly genuine crystals of protein, which possess all the essential 

 features of ordinary crystals, but which in addition have the property 

 of swelling in contact with water. According to Schimper, all protein- 

 crystals belong either to the regular {e.g. the cubical crystalloids of the 

 Potato) or to the hexagonal {e.g. the rhombohedral crystalloids in the 

 endosperm of Bertholletia excelsa) system. While such crystalloids are 

 principally found in dry storage-tissues, where they occur as inclusions 

 of aleurone-grains, they are also quite frequently to be met with in 

 succulent storage-organs {e.g. the Potato), or even in living tissues 

 which are not specially concerned with storage. Zimmermann states 

 that they are especially prevalent as inclusions of the nuclei in the 

 Oleaceae, Sceophulariaceae and Bignoniaceae, and among Pterido- 

 phyta ; their frequent occurrence in chromatophores has been referred 

 to on a previous occasion (p. 37). Crystalloids may also be freely 

 suspended in the protoplasm, especially in epidermal cells and photo- 

 synthetic elements. The wide distribution of these structures is 

 scarcely surprising, in view of the fact that every living cell may 

 accumulate a temporary store of plastic materials for its own use. 



