METABOLISM IN LIVING PLANTS. 



457 



Of the various sorts of building materials, the albuviens must first be con- 

 sidered; they are to be reckoned as the most important constituents of living 

 protoplasm. Although their chemical composition has not as yet been ascertained 

 with complete certainty, it is known that, besides the carbohydrate constituents, 

 albumens contain nitrogen and 08-1 "7 per cent of sulphur; that carbon with 



Fig. 123.— Crystals and Crystalloids. 



' Vertical section through a fallen leaf of the Virginian Creeper (Ampelopsis hederacea). In some of the cells are chistered- 

 crystals, in others bundles of needle-shaped crystals (raphides); in one cell there is a single envelope-shaped crystal. 

 ^^ Solitary and clustered crystals and raphides of oxalate of lime; more highly magnified. « Sphere-crystals in the 

 interior of a swollen bladder-like hypha, with small clustered crystals on the outer side of the hyphal thread ; from 

 Phallus caninus. ' A single needle from a bundle of raphides. » Section of a portion of a Potato-tuber with crystalloids 

 and starch-grains in its cells. » Crystalloids in the cells of a gland on a Potato-leaf, lo-i^i Crystalloids in aleurone grains. 

 13, 1* Globoids in aleurone grains i*. is Isolated crystalloids, lo-i' From the seed of Jlicinus communis ; very highly 

 magnified. 



many, perhaps with more than a hundred, atoms takes part in the construction 

 of a molecule, and that consequently the molecules of albumen are very large. 

 In order that a carbohydrate may become transformed into an albuminous body, 

 nitrogen and sulphur, at any rate, must be drawn into the combination. Nitrogen 



