PROCESS OF STORAGE 1 83 



seeds of grasses. These give the sticky character to dough 

 made from wheat and rye flour. 



All of the above-named proteids belong to the readily diges- 

 tible class. Another class of proteids called nucleins are not 

 so easily digestible, and some of them are apparently not at 

 all so. These can be -isolated by, subjecting cells or tissues 

 containing them to the action of pepsin and other proteid- 

 digesting enzymes, since they remain intact after the other pro- 

 teids have gone into solution. The nucleins are insoluble in 

 water and dilute acids, but they dissolve readily in alkaline solu- 

 tions. They invariably contain phosphorus and frequently 

 iron, but not all have sulphur. They always occur in the nucleus, 

 and possibly to a certain, extent in the cytoplasm. 



Amides. — The amides contain carbon, hydrogen, nitrogen, 

 and oxygen, and are simpler nitrogenous foods than the pro- 

 teids. All amides appear to be soluble in the cell-sap, though 

 not with equal ease. They occtir as reserve food chiefly in 

 underground parts, such as fleshy roots, bulbs, tubers, and 

 rhizomes; and in these places nearly the whole of the reserve 

 nitrogen may be in amide compounds, such as asparagin, glu- 

 tamin, tyrosin, and leucin. Of the nitrogen occurring in the 

 beet root and potato, 30 per cent, and more is in the form of 

 amides. Asparagin is the most common form in which nitroge- 

 nous foods are distributed throughout plants, and when seeds are 

 germinating their proteids gradually are reduced for the most 

 part to this form. 



The Process of Storage. — The leaves being the organs in 

 which the non-nitrogenous, and apparently a good part of the 

 nitrogenous, foods are made from the raw materials, the stor- 

 age tissues, in whatever part of the plant, must get from the 

 leaves in soluble and transportable form the foods which they 

 are to store up. 



As has been said, the non-nitrogenous foods travel to the 

 storage tissues chiefly as glucose, and the nitrogenous for the 

 most part in the form of asparagin. Arrived at the storage 

 tissues these relatively simple, soluble, and diffusible forms of 



