146 THE ELEMENTS OF VEGETABLE HISTOLOGY 



Alkaloids. The alkaloids are seldom visible in 

 plant cells and their presence is usually demonstrated 

 by the addition of mineral acids which form crys- 

 talline salts. 



Glucosides. Glucosidal substances may or may 

 not be visible in plant cells without special treatment. 

 Those glucosidal substances which do occur in visible 

 form show such great variations in character that 

 general descriptions cannot be given. The deposits 

 of the glucoside, hesperidin, in buchu leaves are illu- 

 strated in Plate 52, No. 3. 



Calcium Oxalate. This material may occur in 

 almost any part of the plant and, with the exception 

 of starch, is perhaps the most important cell content 

 from the standpoint of the analyst. Calcium oxalate 

 occurs in needles, rosettes and various other crystal- 

 line forms. The types of crystals recognized are 

 acicular, rosette, prismatic and micro-crystals (crypto- 

 crystalline crystals). Acicular or needle-like crystals 

 may occur singly or in bundles termed raphides. 

 Rosette crystals are aggregates of small prismatic forms. 

 The prismatic forms of calcium oxalate are modi- 

 fications of the monoclinic and tetragonal systems. 

 Perfect crystals are the exception rather than the 

 rule, although those of cubical or monoclinic form 

 may be fairly symmetrical. Micro-crystals are the 

 smallest type of plant crystal, and, although they 

 are usually plentiful when present, are often difficult 

 of recognition because of their small size. These 

 crystals occur as triangular prisms and appear as 

 V-, Y- and T-shaped forms, according to the crystal 

 angles exposed to view. Crystal sand consists of 

 minute micro-crystals or the broken fragments of 



