772 A TEXT-BOOK OF BOTANY. 



plant products are usually said to be calcium oxalate. This sub- 

 stance is insoluble in water, alcohol, and acetic acid, soluble in 

 the mineral acids and occurs usually in definite crystals. These 

 crystals are rather easily studied in Iris, Ouillaja, etc. (see page 

 i86). They are found to crystallize either in the tetragonal or 

 monoclinic systems, sphenoids of the latter being present in 

 Belladonna (see pages 183-192). 



Some substances occur in a crystalline form even upon the 

 commercial product, as vanillin upon vanilla pods and cumarin 

 upon tonka seeds ; or crystals may be found in special cells, as 

 piperine (Fig. 424) in Piper album a.nd Piper nigrum. In alco- 

 holic material, particularly of the Compositae, characteristic sphero- 

 crystals are found, as in inula (see pages 150-154). Sometimes 

 similar sphero-crystals are observed upon soaking the drug of 

 commerce in water and then adding alcohol, as in Scilla. Again, 

 crystalline substances separate upon the addition of mineral acids, 

 as when nitric acid or sulphuric acid is added to sections of 

 Hydrastis (Fig. 95). Again, upon dissolving the product either 

 in water, as with catechu, or in solutions of chloral, as with 

 gambir, a crystalline residue remains. Finally, upon extracting 

 the dried plant with suitable solvents, as Prollius' solution, and 

 evaporating the solvent, characteristic crystals separate, as with 

 coca, hydrastis, nux-vomica, cinchona, cola, guarana, etc. ; or 

 distinct crystalline precipitates may be obtained upon the addition 

 of special reagents, as palladous chloride to solutions containing 

 cocaine hydrochloride (Fig. 97), or gold chloride to solutions 

 containing caffeine (Fig. 96). Attention has already been directed 

 to the fact (pages 173-176) that quite a number of plant principles 

 are capable of being sublimed. 



For some time past, in the study of certain of the cryptogams, 

 as bacteria, yeasts, and fungi, there has been a disposition to rely 

 upon physiological rather than morphological characters, this 

 being due not only to the fact that these are more constant and 

 characteristic in these organisms, but also to the fact that distinct 

 morphological characters are entirely wanting in some cases. 

 While the necessity for this additional study in the higher plants 

 is not so apparent on account of the presence of well-defined 

 morphological characters, still the value of physiological marks 



