184 STORAGE OF FOOD AND WATER 



food either accumulate there in the same form in which they 

 came, or, as more often occurs, they are converted into more 

 complex, less diffusible, or entirely insoluble forms. 



Glucose, for instance, may simply accumulate as glucose, as 

 in the onion, or it may be condensed into the less diffusible 

 saccharose, as in the root of the sugar beet; or it may be con- 

 verted into insoluble starch, as in the potato, or into oil, as in 

 oily seeds. 



Asparagin may be stored as it is or first changed to some 

 other amide such as leucin, tyrosin, and glutamin, as is the 

 case in the roots, tubers, etc., of various plants. Or asparagin 

 may be condensed into some form of proteid, in which case 

 salts of sulphur and phosphorus may also cooperate. 



In these processes of transformation the various cell organs 

 (nucleus, general cytoplasm, plasmatic membrane, plastids) 

 play different, though not independent parts. Thus, the leuco- 

 plasts make starch from glucose, and apparently the cytoplasm 

 makes oil from glucose, and proteids from asparagin; and in all 

 of this work it is almost certain that the nucleus lends a hand. 



We conclude that the leucoplasts make the starch because 

 it first appears as a very minute granule within the leucoplastic 

 body and gradually attains to its full size there. The leuco- 

 plasts absorb the glucose and readjust its elements into the 

 more complex starch. We note the fact but cannot tell how 

 it is accomplished, nor the steps in the process. As fast as 

 the glucose is thus taken out of solution more comes to the 

 leucoplasts by diffusion, and the process advances until the 

 leucoplasts are stretched to an almost or quite invisible film 

 outside the starch grain. 



If the starch grain makes its beginning at the center of the 

 leucoplast the successive layers are about of equal thickness 

 all around and the grain becomes concentrically striated, as 

 in the garden bean; but if the grain starts outside the center 

 the additional layers are formed faster, and so become thicker, 

 on the side of the greater amount of leucoplastic substance, as 

 we find them in the Irish potato (Fig. loi). 



