242 NUTRITIVE METABOLISM 



of chemical compounds is characteristic of the greater number 

 of vegetal organisms. Surplus material is conducted away from 

 the point of formation, and generally deposited in the tissues in 

 some form not readily diffusible. Such deposition may be made 

 in spores, thalli, roots, stems, branches, leaves, floral organs, seeds 

 and fruits, etc. The general purpose of such accumulation is 

 to afford nutriment to the "growing cells in the succeeding vege- 

 tative period. A great many instances might be cited how- 

 ever, in which the food-material placed in a fruit actually serves 

 only to attract animals which consume it, and carry the seeds to 

 other possible habitats. Again reserve materials may be poison- 

 ous to animals and thus serve no other purpose than that of gen- 

 eral protection. 



Starch is the most abundant and widely distributed reserve 

 substance. It may be formed by the action of the chloroplasts 

 or by other plastids (leucoplasts) in various parts of the body, 

 and is an extremely economical substance for storage purposes. 

 It is not formed by the fungi, although the plastids of chloro- 

 phylless seed plants are capable of constructing it from other 

 carbohydrates. Glycogen, a carbohydrate closely related to 

 starch, is formed in the fungi, and is generally in solution in the 

 cell-sap although sometimes deposited in amorphous form. Inulin 

 is a reserve carbohydrate found in Compositae, Liliaceae, Amary- 

 lidaceae and other Monocotyledons. Cane sugar is used as a 

 reserve food in the sugar beet, and sugar cane, and grape sugar 

 is stored in many forms. Layers of reserve cellulose are depos- 

 ited on the walls of cells, especially in seeds, of which the common 

 date of commerce affords a good example. Proteids are stored 

 in the form of aleurone grains, and in crystals. Gluten occurs 

 in the seeds of certain grasses. Amides, such as asparagin, are 

 to be found in the sap of many plants, although in most instances 

 it is simply the transitory form of the more complex proteids. 

 Glucosides are particularly abundant in the Cruciferae and allied 

 orders. Fats and oils are abundant in seeds and also are often 

 found in fleshy roots. These substances, like starch, are gener- 



