BODY AND BRANCH DISEASES AND INJURIES 53 



bark so rapidly that it scales o£F and does not give the lichens 

 time to become established in abundance. Both the foliaceous 

 and crustaceous forms of lichens are found growing on bark, 

 often to the extent that they entirely cover the trunk and 

 limbs. The common supposition is that they are responsible 

 for the poor condition of the trees on which they occur, but for 

 the reason just stated it seems more likely that the tree is 

 covered with lichens because it is slow-growing. 



It is supposed, since the lichens do not penetrate the bark 

 and establish any true parasitic relation with the tree, that 

 any damage they cause is due to their mechanical interference 

 with the respiration and transpiration processes which go on 

 through the lenticels in the bark. The effects of shading and 

 continuously holding moisture may be considered to increase 

 the damage caused by lichens; consequently the crustaceous 

 forms seem to be more injurious because they grow more tightly 

 appressed to the bark. 



The eradication of lichens can be easily accomplished by 

 spraying the affected parts in the ordinary way with bordeaux 

 mixture. The lichens will die within a few days. The best 

 results are obtained if the spraying is done when the leaves 

 are off the tree, since all parts of the infested trunk and limbs 

 can be more surely and easily reached with the mixture. For 

 directions for making bordeaux mixture, see page 358. 



Rbfekences 



Waite, M. B. Experiments with fungicides in the removal of lichens 

 from pear trees. Joiir. Mycology 7 : 264-268, pis. 30-31. 1893. 



Hartig, R. Pseudo-parasites. In Text-book of the diseases of trees, 

 pp. 35-36. 1894. 



Slime-Flux 



Caused by the fermentation of oozing sap 



Wounds of various kinds, in such trees as birch, elm and maple 

 which bleed very profusely, may develop a chronic exudation 



