240 Minnesota Plant Diseases, 



means the wood is thoroughly impregnated and the salts de- 

 posited, not only in the cavities, as with most other substances, 

 but also in the walls of the cells. This process has not yet been 

 thoroughly tested but has apparently many excellent features 

 which may perhaps, in the future, make it a valuable treatment. 

 Other processes, either new or imperfectly known, may merely 

 be mentioned here. In one electricity is utilized and is passed 

 through the timber in a solution of magnesium sulphate. Two 

 things are claimed for this treatment : cheapness and a com- 

 plete distribution of the impregnating salt. Another method is 

 directed toward a saving of expense in the pure creosote meth- 

 od by using an emulsion of the oil in resin and a strong solution 

 of soda lye. This has again been modified by the substitution 

 of formalin in the place of the lye. 



The following list of timber rots and timber-tree diseases is 

 by no means complete for the wound parasites and timber rots 

 of Minnesota ; but it includes many common forms and above 

 all is intended to give the reader an idea of the kind of organ- 

 isms responsible for the rots of timbers and the deaths of timber 

 trees. Other related forms will be readily recognized by their 

 general similarities with these forms. The general preventive 

 methods have been mentioned above. Only in special cases 

 are additional measures given. 



Stereum wood rot (Stercum species). On the dead trunks of 

 many of our broad-leaved trees, can often be found numerous 

 shelf-like fungi projecting in the manner of the pored shelves. 

 In some species the upper surface is rough, hairy or silky, and 

 the under surface is smooth. The latter does not contain pores 

 as in the true pore-fungi. The shelves are usually of a leathery 

 consistency and in dry weather often curl up, expanding again 

 in wet weather. The spores are borne on typical basidia in pal- 

 isades which cover the under surface. In some cases, instead 

 of shelf-like bodies, prostrate, crust-like objects are formed 

 which are sometimes turned back at the margins. In these 

 cases the spores are found on the upper surface of the prostrate 

 body. There are several species of this genus which are de- 

 structive parasites of our forest trees. Oaks are very often at- 

 tacked. The fungus usually gains entrance through wounds 

 and grows outward from that point. Fig. 117 shows an oak 



