282 PRINCIPLES OF GARDENING. [CH. VIII. 



magnifier exhibits the crj^stals in the forms of 

 rhomboids and four sided prisms. When the liquid 

 is dark coloured, the bark appears blackish, and 

 seems as if coated \^dth varnish. It sometimes is dis- 

 charged in such quantities as to hang from the bark 

 like stalactites. The matter of which these are 

 composed is alkaline, soluble in water, and with acids 

 effervesces. The analysis of this dark slimy matter 

 shews it to be compounded of carbonate of potass 

 and ulmin, a product peculiar to the elm. The white 

 matter deposited round the canker was composed of — 



Vegetable matter . . . 60.5 



Carbonate of potass . . 34.2 



Carbonate of lime . . 5.0 



Carbonate of magnesia . 0.3 



100.0 

 Vauquelin calculated from the quantity of this 

 white matter that was found about the canker of an 

 elm, that 5001b. weight of its wood must have been 

 destroyed a. There is no doubt that such a discharge 

 is deeply injurious to the tree, but the above learned 

 chemist appears to have largely erred, for he calcu- 

 lated from a knowledge of the amount of the saline 

 constituents in the healthy sap, whereas in its 

 diseased state these are much and unnaturally 

 increased. I once was of opinion, that this disease 



' Annales de Chimie, xxi. 30. 



