PROTEINS 



51 



The proteins of oil-containing seeds {e.g. Castor Oil, Brazil- 

 nut) occur in the form of especially large granules, known as 

 aleitrone grains. These appear to arise, as the seed dries during 

 ripening, from the entire contents of vacuoles rich in protein- 

 substance. Although the structure of aleurone grains is relatively 

 complicated, they exhibit the characteristic protein-reactions 

 mentioned above. If a thin section of the Castor Oil or Brazil- 

 nut (from which the fat has been removed by soaking in alcohol 

 and benzene respectiveh") be stained with iodine, the brown- 



FiG. 23. — Aleurone grains {AL] from the endosperm of the Castor Oil 

 plant [Ricinus) showing the globoid (GI.) and cr^-stalloid [Cr.). 



coloured grains are readilv seen under the microscope. Each 

 shows a bounding membrane, the original membrane of the 

 vacuole, enclosing amorphous protein in which two or more 

 bodies are embedded. One of these, the crystalloid (Fig. 23, Cr.), 

 is large and more or less angular, whilst the other, the globoid, 

 is smaller and rounded (Fig. 23, Gl.) : both consist of protein, 

 but in the globoid, of which more than one may be present, 

 this is combined with a double phosphate of calcium and mag- 

 nesium. Bv mounting sections in water the amorphous ground- 

 mass of the aleurone grain mav be dissolved, and the bounding 

 membrane rendered clearlv visible : on the other hand, treatment 



