136 THE ELEMENTS OF VEGETABLE HISTOLOGY 



and is usually stored in those seeds which contain 

 large amounts of oil but are lacking in starch. In 

 the synthesis of nitrogenized nutrients oxalic acid is 

 formed, and this poisonous substance must be disposed 

 of. The oxalic acid reacts with the calcium salts 

 present, resulting in the formation of calcium oxalate, 

 which because of its insolubility is practically harm- 

 less. Calcium oxalate occurs in various crystalline 

 forms and is of service in the identification of certain 

 vegetable materials. By complex and little under- 

 stood syntheses, hydrocarbon nutrients may possibly 

 be produced from soluble starch. 



Glucosides are substances which, upon digestion 

 with dilute mineral acids, readily decompose, yielding 

 glucose as one of the products of the reaction. Many 

 glucosides are extremely poisonous and, aside from 

 the fact that they may protect the plant against 

 animal attacks, little is known of their exact function 

 in the plant economy. 



The soluble carbohydrates may be transformed 

 by substances within the cell into reserve cellulose. 

 The reserve cellulose is deposited upon the original 

 thin cellulose wall of various cells, resulting in the 

 formation of collenchymatic tissue. 



SECRETING CELLS AND CAVITIES 



Secreting cells are concerned in the synthesis of 

 resins, gums and volatile oils. While these sub- 

 stances are formed from the products of assimilation 

 they are not as intimately concerned in the nutrition 

 of the plant as are the substances noted in the pre- 

 ceding section. The plant tissues performing this 



