92 VEGETABLE SUBSTANCES. 



by giving the protein reaction, by their solubili- 

 ty in ammonia, dilute potash, or acetic acid, 

 and by swelling in water. They are often insol- 

 uble in a potash solution of above ten per cent. 

 There are also some which are soluble in a solu- 

 tion of table-salt (p. 32). As a characteristic 

 which is always useful, though not of a chemical 

 nature, we mention further the inconstancy of 

 their angles. 



The red, somewhat doubly refractive, tabular 

 crystalloids of certain Florideae that have been 

 kept in the herbarium or mounted in glycerine 

 are especially noteworthy. They are the so-called 

 rhodospermin crystals of Cramer, and are in- 

 soluble in sodic-chloride, in which they lose their 

 color. 



The crystalloids contained in protein grains be- 

 come visible only after treatment with warm 

 glycerine. 



CAOUTCHOUC 



Occurs in the latex of different plants in the form 

 of small homogeneous globules, which swell in 

 ethereal oils, and are soluble in carbon bisulphide, 

 chloroform and benzole, but are not attacked by 

 dilute acids or alkalies. 



Pflanzen, Strassburg, 1879. J- Klein: Krystalloide der Meeresalgen. 

 Flora, 1880, p. 65. Cohn's Beitrage zur Biol. d. Pfl., 1880, III., p. 163 

 (Crystalloids in the nuclei of Pinguicula alpina). 



1 Weiss: Allg. Dot, I., p. 191. Duchartre: Elements de Bot., 1877, 

 p. 74. 



