144 BOTANICAL GAZETTE [AUGUST 
crystals so constructed and placed as best to resist vertical and diago- 
nal pressure, as of soil particles and the weight of the bean. 
In the case of acicular crystals, so prevalent in monocotyls, it is 
evident that they give elasticity as well as support against crushing 
pressure. This applies especially to the very long and comparatively 
thick needles of calcium oxalate found in squill, iris, and other mem- 
bers of the lily family. These crystals (raphides) are especially com- 
mon in the parenchyma of roots, rhizomes, tuberous roots, stems, and 
leaves. 
It is generally admitted that the cystoliths of Ficus leaves, etc., 
perform a purely mechanical function. In plant organs subjected 
principally to a radial pressure, as are thick roots, tubers, thick rhi- 
zomes, etc., not specially supplied with mechanical elements, the 
aggregate crystals predominate, ¢. g., Rheum and Rumex. In such 
organs as potatoes, corms of Colchicum, etc., the necessary mechanical 
support is given by the starch which fills the cells. A potato free 
from starch would be crushed by the soil in which it grows. 
Further evidence in favor of the mechanical support theory of 
calcium oxalate is to be deduced from the fact that in many instances 
the crystals are imbedded in a gelatinous or mucilaginous substance 
which equalizes the pressure exerted, acting as a bumper between cell- 
wall and crystal. In other instances the cell-sap takes the place of the 
mucilage. 
It is very frequently found that cells bearing calcium oxalate take 
the place of mechanical cells in leaves. The crystals are especially 
common in the cells bounding the air chamber of stomata which cer- 
tainly require some mechanical support. 
It is also highly probable that calcium oxalate is merely accident- 
ally present in some plants and plant organs, but in the majority of 
instances its presence points toward a function of mechanical sup- 
port as indicated.— ALBERT SCHNEIDER, Worthwestern University School 
of Pharmacy, Chicago. 
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