METAIJOLISM IN LIVING PLANTS. 



457 



Of the various sorts of building materials, the albumens 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 0'8-l"7 per cent of sulphur; that carbon with 



Fig. 123.— Crystals and Crystalloids. 



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

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

 2-ä Solitary and clustered crystals and raphides of oxalate of lime; more highly magnified. « Spliere-ci-ystals in the 

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

 PhalUts caninus. ^ A single needle from a bundle of raphides. 8 Section of a portion of a Potato-tuber with crystalloids 

 and starch-grains in its cells. 9 Crystalloids in the cells of a gland on a Potato-leaf. ^0-^2 Crystalloids in aleurone grains. 

 13. 14 Globoids in aleurone grains 1^. i^ Isolated crystalloids. 10-I6 tVom the seed of Kicinus 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 



