164 VEGETABLE PHYSIOLOGY 



albumin. There is no evidence at present that they are 

 stages in the constructive process. 



Some of the proteoses occur in certain seeds in associa- 

 tion with some of the globulins. Both the albumins and 

 the globulins, and probably the meta-proteins as well, are 

 transformed into proteoses and peptones by the action of 

 hydrolysing agents, such as dilute mineral acids and certain 

 secretions of the protoplasm known as enzymes, whose 

 action will be treated of in a subsequent chapter. 



Besides these classes of proteins, another occurs which 

 presents the curious peculiarity of being soluble in alcohol. 

 Proteins of this group have been extracted from the endo- 

 sperm of some of the cereal grasses. Examples of them 

 are found in the zein of maize ; and the gliadin and 

 glutenin of wheat flour. Zein differs from the crystallised 

 protein of the hemp in its comparatively low content of 

 nitrogen, which amounts to only 16*13 per cent. It dissolves 

 easily in alcohol of about -820 specific gravity, but is 

 insoluble in absolute alcohol. It is insoluble also in water, 

 but in mixtures of alcohol and water it dissolves to a 

 greater or less extent, being most easily soluble in a mixture 

 containing about 90 per cent, of the spirit. In one of a 

 lower concentration than 50 per cent, it is very sparingly 

 soluble. Zein can be. dissolved by glycerine if heated to 

 150 C. ; also by glacial acetic acid and by dilute solutions 

 of caustic potash. Like other proteins, it is converted into 

 peptpne by pepsin and hydrochloric acid. 



The original construction of protein matter, like that 

 of carbohydrates, seems to be carried out only by 

 vegetable protoplasm. It does not, however, appear to be 

 dependent upon the same conditions as the process already 

 described. It cannot be classed with the latter as a process 

 of photosynthesis, and it is only indirectly dependent 

 upon the action of the chlorophyll apparatus. Unlike the 

 construction of carbohydrates, it is not confined to green 

 plants indeed the fungi can commence the synthesis at a 

 lower stage than the latter, beginning the construction with 



