214 THE CONSTITUENTS OF PLANTS. IX. 



According to Halliburton" the vegetable proteids may be 

 classified as follows : 



(a) Vegetable albumens, which are soluble in water and 

 coagulate at 70. These have been isolated from rye, 

 wheat, potatoes, and other plants. 



(b) Vegetable globulins, insoluble in water, soluble in saline 



solutions ; coagulate from 55 to 75. The crystallizable 

 proteid just alluded to (vitellin) is a globulin. An 

 analysis of this substance gave the following numbers : 



Carbon. Hydrogen. Nitrogen. Sulphur. Oxygen 



52-43 7-12 18-10 0-55 21-80 



(c) Vegetable albuminates. Of these, legumin or vegetable 



casein is the most important. It is found in peas, 

 vetches, beans, and lentils. It is soluble in water and 

 yields on analysis : 



Carbon. Hydrogen. Nitrogen. Sulphur. Oxygen. 



51-48 7-02 16-77 0-40 24-32 



A similar substance obtained from almonds and 

 lupines contains more nitrogen. Hoppe-Seyler states 

 that the albuminates are not present in the plants, 

 but are formed by the action of the alkali used in ex- 

 tracting the proteids. 



(d) The vegetable proteases. These substances are inter- 



mediate in the formation of peptones from proteids. 

 They differ very slightly from the peptones, being, like 

 them, soluble and slightly diffusible. They are precipi- 

 tated by nitric acid, but soluble in excess. They are 

 common in aleurone grains. 



(e) Vegetable peptones. These are very soluble in water and 



diffusible ; they are precipitated by tannin or by abso- 

 lute alcohol. Peptones do not exist in plants except 

 transiently, being probably formed by the action of fer- 

 ments upon the proteids, enabling these bodies to pass, 

 by diffusion, to the growing portions of the organism. 



(f ) Insoluble vegetable proteids. The most important mem- 



ber of this group is gluten, a tenacious, tasteless, 

 brownish grey substance, soluble in strong acids or 

 alkalies. It consists of two substances, one soluble in 



* Watts's Diet, of Chem., Vol. IV., p. 336. 



