PROTEINS IN DIFFERENT PARTS OF PLANTS 9 



similar to the nucleoproteins and nucleins are also obtained from this 

 embryo meal. 



Thus Osborne and Voorhees (366) \cf. also Frankfurt (125) and 

 O'Brien (297)] found that the flour of the entire kernel of samples of 

 spring and winter wheat yielded the quantities of the proteins enumer- 

 ated in the following table: 



Spring Wheat Winter Wheat 



per cent. per cent. 



Glutenin . 4'68 4-17 



Gliadin . 3-96 3 'go 



Globulin . 0-62 0-63 



Albumin . 0-39 0-36 



Protcose 



o-2i 



Osborne and Campbell (336) obtained from the wheat embryo meal 

 no gliadin or glutenin, 10 per cent, of albumin, 5 per cent, of globulin 

 and about 3 per cent, of proteose. The embryo meal contains a 

 relatively large proportion of nucleated cells and therefore a large 

 amount of nucleic acid, which was extracted in combination with the 

 proteins, though much remained in the meal residue in insoluble com- 

 bination with the remaining protein. In view of these facts there can 

 be little doubt that much of the globulin, albumin and proteose ob- 

 tained from the entire seed was originally present in the tissues of the 

 embryo, although a part, possibly, was yielded by the very small amount 

 of protoplasm in the endosperm cells. Similar conditions must cer- 

 tainly exist in other seeds, and the proteins that are found only in very 

 small quantity in the extracts of many seeds may be derived from the 

 embryo and protoplasm and are not to be regarded as a part of the 

 reserve protein of the seed. Thus, for instance, the hemp-seed, which 

 yields a large part of its protein in the form of crystalline edestin, also 

 yields a very small quantity of one or two other proteins coagulated 

 by heating the extracts to about 80, which latter are probably not a 

 part of the reserve protein of this seed. 



The proteins of seeds have been the subject of extensive investiga- 

 tion, and we now know much concerning the chemical and physical 

 properties of a number of different proteins from several species of 

 seeds. Most of these, which are unquestionably the reserve proteins 

 of these seeds, are products of the metabolism of the plant, and, in the 

 fully ripe seed, no longer take part in its physiological processes. They 

 may, therefore, be regarded as in a sense analogous to excretory pro- 

 ducts, for, as Pfeffer has said (603), " All protoplasmic secretions which 

 appear externally and are lost to the plant or which can take no further 

 part in metabolism are to be regarded as excretory substances ". 



In many ways the reserve seed proteins bear a relation to the 



