212 LETTERS ON TREES. 



as some have fancied, in the felHng of the tree at a 

 time when it is full of sap, — as in the ill-developed 

 and ill-conditioned woody-tissue, the produce of the 

 diseased plants of a particular year or series of years? 

 Such tissue, it is conceivable, may be as perishable in 

 its degree and as prone to decay as the diseased potato- 

 tuber, but the tendency thereto be prevented, as long 

 as the tree is in the ground and growing, by the more 

 complete exclusion of the tissue from external agencies 

 than does or can obtain in the case of the latter — an 

 exclusion becoming every year still more complete 

 and perfect by the deposition of new woody-tissue 

 around it, breaking forth, however, after the tree has 

 been felled, sawn up, and exposed to air and mois- 

 ture — to the latter especially. It would, I think, be 

 worth while to examine microscopically and otherwise, 

 the timber of trees which are known at a certain 

 period of their growth to have been diseased, and to 

 compare the woody tissue of the cylinders of the 

 several years. There are marked organic differences, 

 easily detected by the microscope, and sensible chemi- 

 cal peculiarities elicited by analysis, between the tubers 

 of healthy and diseased potatoes. And like or equally 

 notable differences may exist in the woody tissue of 

 diseased and healthy tree-plants. — I am, &c. 



