192 HOW CROPS GROW. 
In the root of the young bean, Sachs found a ring of cells, 
containing crystals of sulphate of lime. (Sitzwngsberichte 
der Wien. Akad., 37, p. 106.) 
Bailey observed in certain 
parts of the inner bark of the 
locust a series of cells, each 
of which contained a crystal. 
In the onion-bulb, and many 
Fig. 24. Fig. 25. other plants, crystals are 
abundant. (Gray's Struct. Botany, 5th Ed., p. 59.) 
Instances are not wanting in which there is an obvious 
excretion of mineral matters, or at least a throwing of 
them off to the surface. Silica, as we have seen, is often 
found in the cuticle, but it is usually imbedded in the cell- 
wall. In certain plants, other substances accumulate in 
considerable quantity without the cuticle. A striking ex- 
ample is furnished by Saxifraga erustata, alow European 
plant, which is found in lime soils. 
The leaves of this saxifrage are 
entirely coated with a scaly in- 
crustation of carbonate of lime 
and carbonate of magnesia. At 
the edges of the leaf, this incrusta- ( < 
tion acquires a considerable thick- {'? 
ness, as is illustrated by figure 26, 
a. Inan analysis made by Unger, 
to whom these facts are due, the | > 
fresh, (undried,) leaves yielded to |4 
a dilute acid 4.14°|, of carbonate | 
of lime, and 0.82°|, of carbonate 
of magnesia. 
Unger learned by microscopic Fig. 26. 
investigation that this excretion of carbonates proceeds 
mostly from a series of glandular expansions at the margin 
of the leaf, which are directly connected with the sap-ducts 
of the plant. (Sitzberichte der Wien. Akad., 43, p. 519.) 
