192 



HOW CROPS GROW. 



In the root of the young bean, Sachs found a ring of cells, 

 containing crystals of suljohate of lime. {Sitzungsherichte 



der Wien. Alcacl, 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 oif 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 crustata, a low 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 acqviires a considerable thick- 

 ness, as is illustrated by figure 26, 

 a. In an analysis made by linger, 

 to whom these facts are due, the 

 fresh, (undried,) leaves yielded to 

 a dilute acid 4.14° |„ of carbonate 

 of lime, and 0.82° |, of carbonate 

 of magnesia. 



linger learned by microscopic 

 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. {Sitz''herichte der Wien. AJcad., 43, p. 519.) 



Fi?. 26. 



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