ALEURONE-GRAINS 



417 



Various circumstances, in fact, point to the conclusion that protein 

 crystalloids always represent reserve-materials, even when they are found 

 in cells other than those belonging to the storage-system. From among 

 the numerous observations bearing upon this question we may select 

 those of Stock for special mention. Stock finds that crystalloids are 

 dissolved in dying leaves, and that they also disappear from plants 

 grown in nutrient solutions containing insufficient quantities of nitrogen. 



Aleurone-grains (Fig. 163) constitute another characteristic 

 form of reserve protein. 197 A typical 

 aleurone-grain is a rounded granular 

 body, the ground-substance of which, 

 according to Tschirch and Kritzler, con- 

 sists mainly of globulins soluble in water. 

 In starchy seeds the aleurone-grains are 

 usually small and lie crowded together in 

 the interstices between the starch-grains 

 and the protoplasmic mesh work. In fatty 

 seeds, on the other hand, they are generally 

 large, and often contain a variety of in- 

 clusions, such as crystals of ealciuin-oxalate, 

 and the small rounded or botryoidal masses 

 known as globoids. According to Pfefl'er, 

 a globoid consists of a double phosphate of 

 calcium and magnesium, combined with 

 certain organic substances. Very often 

 one or more crystalloids also lie embedded 

 in the amorphous matrix of the aleurone 

 grains ; these become clearly visible when 

 the ground-substance is dissolved away by treatment with water {e.g. 

 in Ricinus communis and other Euphoebiaceae). 



Wakker and Werminski state that aleurone-grains are found -in 

 special vacuoles, which at first contain a highly concentrated solution 

 of proteins, but dry up as the seed ripens : during germination the 

 aleurone-grains reabsorb water, and once more become converted into a 

 corresponding number of vacuoles, which later coalesce to form a 

 single sap-cavity. 



How far other widely distributed plant-constituents, such as 

 glycosides and fannivs, may serve as plastic reserve-materials is a 

 question which belongs to the field of pure physiology, and which con- 

 sequently falls outside the scope of the present treatise. 



Fig. Ki3. 



A. Cell with aleurone-grains from the 

 endosperm of Ricinus communis (after 

 treatment with alcoholic mercuric 

 chloride solution), x 400. B. A single 

 aleurone-grain from the endosperm of 

 Ricinus communis, showing a crystal- 

 loid and four globoids. x800. C. 

 Aleurone-grain of Elaeis guianensis, 

 mounted in oil. x 500. D. Aleurone- 

 grain from the cotyledon of Bertholletia 

 excelsa, fixed with alcoholic mercuric 

 chloride and mounted in water, x 500. 

 After Pfeffer. 



L'l) 



