LOCATION AND EXTENT OF STORAGE TISSUES 187 



rone grains), as in the seeds of castor oil and garden bean. In 

 the early stages of development of these seeds no aleurone grains 

 are present, but later minute projections from the meshes of 

 the cytoplasm appear which gradually increase in size and fill 

 up the interstices. The cytoplasm thus seems to be the imme- 

 diate agent in the construction of the aleurone grains. Whether 

 the cytoplasm breaks down its own substance to form the aleu- 

 rone or constructs this directly from amides, sugars, and salts 

 of sulphur and phosphorus, has not been determined. It is 

 possible, of course, that both methods are employed; l)ut what- 

 ever the steps in the formation of reserve proteids, the simpler 

 amides, sugars, etc., that are known to flow to the storage cells 

 during the storage period contribute the necessary elements. 



Characteristics of the Storage Tissues. — Tissues pri- 

 marily designed for the storage of food, as the endosperm of 

 seeds and the bulk of the tissues in fleshy roots, tubers, etc., 

 have relatively large cavities and thin cellulose walls, or where 

 the walls are much thickened they have many thin places in 

 the form of pits. Storage being a vital function the storage 

 tissues are composed of living cells and when these cells die 

 they are no longer functional. Since most of the stored food 

 must be digested before it can be moved from its place of storage 

 the power to make digestive ferments or to carry on digestion 

 directly without the aid of ferments must be one of the leading 

 characteristics of the protoplasts of the storage tissues. When 

 starch is to be stored the cells must be provided with abundant 

 leucoplasts. 



Location and Extent of Food Storage Tissues. — Food 

 may be stored for longer or shorter periods in any living cell, 

 but there are certain tissues which have the storage of food 

 for their chief function. These are the endosperm and peri- 

 sperm of seeds, and sometimes the mesophyll of cotyledons; 

 the medullary rays and wood parenchyma of ordinary stems 

 and roots, and of fleshy roots and stems where the rays and 

 wood parenchyma greatly preponderate over the other tissues; 

 that portion of the pith immediately bordering the wood, and 



