DISEASES OF TREES 



then it is our duty to direct attention to these. This I have 

 never neglected to do, and, although I do not under-estimate the 

 many difficulties which foresters will long have to encounter 

 in endeavouring to put into practice the 

 results of scientific investigation, still I hold 

 that, as the guardians of the forest, it is their 

 duty to make themselves acquainted with the 

 results of scientific investigation, and care- 

 fully to watch over the health of what is 

 committed to their charge. Not only must 

 they do everything that may prevent disease, 

 but they must also instantly adopt energetic 

 measures to nip an existing disease in the 

 bud, and so prevent its further spread. 



As every disease must necessarily be treated 

 differently, this is not the place to enter on 

 the consideration of specific measures. But 

 just as human health is better maintained by 

 the observance of certain general laws, so 

 there are also general rules for the treatment 

 of woods, by following which we may pre- 

 serve the health of the trees. 



The best prophylactic measure against the 

 occurrence and spread of an epidemic is 

 the formation of mixed woods. Infection, 

 both below and above ground, is least likely 



FIG. 13. Portion 

 of a tracheid of 

 Pinus decomposed 

 by P o lyp oru s 

 Schiveinitzii. Most 

 of the cellulose has 

 been extracted, the 

 walls consisting 

 chiefly of lignin. 



In drying, cracks to occur when every tree is isolated by being 

 surrounded by others of a different species. 

 On ground which is infested by root-parasites, 

 or which contains resting-spores whose vitality 

 is preserved for many years, it may be advis- 

 able, under certain circumstances, to abandon 

 the cultivation of some particular species of 

 tree. One should also try to prevent the 

 distribution of spores either by men or 



animals, and especially so in the sale and purchase of young 



trees. 



In the case of root-parasites, the therapeutic measures to 



be adopted when a disease has broken out consist partly in 



not extend to the 

 primary wall, a b. 

 These cracks are 

 seen to cross each 

 other at the bor- 

 dered pit t, and at 

 the perforations d 

 andtf; a simple fis- 

 sure is shown at f. 



