768 A TEXT-BOOK OF BOTANY. 



studied were differentiated in a manner that could not have been 

 accomplished by chemical analysis or other methods of procedure. 

 A careful study of much that has been written, and especially 

 of the illustrations that have been made, of micro-crystals in 

 plants and drugs, shows that erroneous conclusions may be easily 

 drawn from the general appearance of crystalline precipitates or 

 aggregates of crystals that are formed. For instance, Vogl has 



FIG. 421. Cubebin: orthorhombic crystals from Prollius* solution, showing various 

 types of twinning (a, b, c); d, amorphous material in the form of oily drops (under-cooled 

 liquid); e, this amorphous material crystallizing in aggregates. 



shown that the sphero-crystals, found in the glandular hairs 

 of Mentha piperita and considered by some to be menthol, are 

 found in leaves of many of the Labiatse. Again, very many sub- 

 stances produce aggregate groups which closely resemble each 

 other, as of citric acid, cocaine hydrochloride, etc. 



In regard to the value of the crystallographic method we 

 quote the following paragraph from Brown (loc. cit.) : "When 

 a chemical compound solidifies from fusion, solution or vapor 

 under conditions which are favorable to the development of 



