SPECIAL METHODS. ZKj 



a dilute aqueous solution of tannin for ten minutes, and 

 then, after careful washing, in 2% osmic acid. The crystal- 

 loids are stained a beautiful brown by these reagents. After 

 washing out the osmic acid, the preparations may be pre- 

 served in glycerine. 



Poulsen (II, 548) places the sections first in alcohol for 

 24 hours, then for an hour in a 25$ aqueous solution of 

 tannin, and finally, after washing this out with water, in an 

 aqueous solution of potassium bichromate, in which he 

 leaves them until they are brown or yellowish. For the 

 preservation of these preparations, in which the aleurone 

 grains should be quite transparent, Poulsen recommends 

 glycerine. 



According to another method also recommended by 

 Poulsen, the sections, treated in the same way with alcohol 

 and tannin, are placed, after washing, for an hour in a 10- 

 20$ aqueous solution of ferrous sulphate. The preparations 

 are then washed and transferred to balsam in the usual way. 

 The crystalloids then appear deep blue, almost black. 



c. The Globoids. 



388. The globoids consist, according to Pfeffer's researches*- 

 (I, 472), of the calcium and magnesium salt of an organically 

 combined phosphoric acid. They do not occur in all protein: 

 grains but, according to Pfeffer's investigations, are not 

 wholly absent from any seed. They are sometimes more 

 or less precisely globular in form, as in Pceonia and Ricinu? 

 (cf. Fig. 49, I and II, g), sometimes irregular, biscuit-shaped; 

 or clustered, as in Bertholletia excelsa (Fig. 50, 1). The rela- 

 tive and absolute size may vary very greatly in the same 

 seed. For example, the protein grains in the innermost 

 layers of the endosperm of Paonia are quite free of glo- 

 boids, while their size increases regularly toward the outside 

 (cf. Fig. 49, I, a-c\ 



389. In oil or Canada balsam the globoids have the 



