CELL<X)NTENTS AND FORMS OF CELLS. 193 



or dilute acids, or by " salting out " by the use of strong or satu- 

 rated solutions of ammonium sulphate, magnesium sulphate, or 

 sodium chloride. (2) The proteins which contain phosphorus are 

 sometimes called phytovitellins, as legumin in peas, which contain 

 -35 P er cent - f phosphorus. A third class of plant proteins, 

 which are alcohol-soluble, are found in cereals, as the gliadin 

 of wheat and rye and the zein of maize. The cohesive and dough- 

 ing properties of wheat flour are attributed to the association of 

 gliadin and another protein called glutenin. 



Some of the plant proteins occur naturally in the crystalline 

 form, either free in the cytoplasm, as in the potato tuber (Fig. in, 

 A}, or as components of aleurone grains, as in the seeds of 

 Ricinus communis and Brazil nuts (Fig. HI, B and D). Phyto- 

 globulins in the form of crystals and spheroids have been obtained 

 from extracts of flax-seed, hemp-seed, Brazil-nut, castor-oil seeds 

 and others. Protein crystals are, according to Wichmann, iso- 

 morphic, and probably belong to the hexagonal system (Fig. 112). 



Aleurone grains are made up of phyto-globulins (formerly 

 called crystalloids), globoids and a ground mass, the whole being 

 enclosed by a membrane-like material. They may be studied by 

 taking advantage of the difference in solubility of the substances 

 composing them. The membrane, or lining of the protoplasm, 

 while soluble in water, remains intact with sections examined in 

 any of the fixed oils, as cotton-seed oil. Usually seeds which 

 contain aleurone are rich in fixed oils, and if this oil is first removed 

 by placing fresh sections in alcohol, or alcohol and ether, the 

 subsequent study is facilitated. If the sections thus treated are 

 mounted in water, the membrane gradually dissolves, leaving 

 the globulins, globoids, and calcium oxalate. On adding a o.i 

 to i per cent, solution of either sodium or potassium hydrate, the 

 globulins dissolve, the globoids and calcium oxalate crystals re- 

 maining unaffected. The' globoids may be dissolved by the use 

 of a i per cent, acetic acid solution, or concentrated solutions of 

 ammonium sulphate or monopotassium phosphate. The calcium 

 oxalate remaining may then be treated with hydrochloric acid in 

 the usual way. 



CLASSIFICATION OF PROTEINS. A committee on protein nomen- 

 clature of the American Society of Biological Chemists proposed 

 13 



