May 6, 1918 Canker of Poplars and Willows 343 



(3) Pure cultures of this fungus were isolated from the diseased areas, 

 and the typical lesions of the disease were produced by inoculating 

 healthy poplar plants with pure cultures of the fungus. The fungus 

 was reisolated from the cankers produced by the inoculations. 



(4) Pure cultures of C. chrysosperma on malt and corn-meal agars were 

 made, and the cultural characters of the fungus determined. 



(5) The fungus enters the host through wounds and dead branches. 



(6) C. chrysosperma is a serious parasite on poplars in the South- 

 west under the following conditions: (a) On trees which are growing 

 at the outer limits of their range and are therefore in a more or less 

 unfavorable environment; (b) on trees planted in streets, lawns, and 

 cemeteries where they have been weakened from neglect and lack of 

 sufficient water; (c) on trees which have been severely pruned, as in 

 pollarding; (d) on cuttings in propagating beds where the usual method 

 of propagation is used. 



(7) The fungus C. chrysosperma occurs in nine States and on 14 different 

 species of trees. It is also found in Mexico and in Europe. 



(8) The best method of controlling this disease is as follows : (a) The 

 most resistant species should be selected; the trees should be given an 

 abundance of water, and should be protected against mechanical injuries; 

 (b) a strict supervision should be established over all nurseries hand- 

 ling poplar stock intended for distribution in the semiarid regions of the 

 western United States; (c) all nursery stock which shows the slightest 

 indication of the disease should be destroyed. 



