338 Journal of Agricultural Research voi. xiii, no. 6 



considered a great luxury, and any person who succeeds in growing them 

 always takes the greatest care not to lose them. The disease seems to 

 be very virulent and is reported to be killing practically all of the Carolina 

 poplars in that region. This illustrates how serious this disease becomes 

 on species of poplar which are growing under unfavorable conditions. 



The canker seems to be widely distributed in North Dakota and is 

 causing serious damage to the poplar groves of that State, according to 

 the following extract from a letter to the writer from State Forester 

 Fred W. Smith : 



The poplar groves in this State are pretty largely infected with Cytospora chrysos- 

 per??ia. This disease seems to be affecting all of the poplars with the exception of the 

 native poplars, P. balsamifera and P. iremuloides var. candicans. The common poplars 

 distributed by the nurseries seem to have been all badly infected. Tens of thousands 

 of trees have been killed in North Dakota this last j^ear by this disease. 



Poplars, Vt'hen planted in dry climates on streets, lawns, and in ceme- 

 teries, are often very subject to the attacks of Cytospora chrysospcrma, 

 especially when the young trees are not watered regularly and abundantly. 

 When the trees do not receive enough water, the twigs and small branches 

 in the top gradually die. Through these dead and dying branches the 

 fungus readily enters. This is especially true of certain species of poplar 

 which are highly susceptible to the disease. Hundreds of shade trees in 

 Arizona, New Mexico, and Texas have been seen by the writer which 

 were either dying or had been seriously injured by this fungus. Most of 

 these trees had been much neglected and undoubtedly had not had a 

 sufficient amount of water. 



In many of the towns of Arizona and New Mexico the habit of pruning 

 large living limbs, and, in some cases, of pollarding the entire tree, is 

 common. When large limbs are cut off in this dry climate, the exposed 

 ends of the portion left on the tree die back from drying some 3 to 12 

 inches. The tree may then put out new branches below the dead por- 

 tion. Later, this young growth is often killed by the gradual advance 

 of this canker which entered at the exposed dead surface of the severed 

 branches. 



The writer has received specimens of Carolina poplar cuttings taken 

 from propagation beds attacked by this fungus. The method usually fol- 

 lowed in propagating trees of the genus Populus in nurseries is to take 

 cuttings about 8 to 10 inches long and 0.25 to 0.5 inch in diameter and 

 place them in the ground with the upper part projecting some 2 to 3 

 inches. Such propagation stock is often seriously damaged by Cytospora 

 chrysosperma. This fungus attacks the exposed ends of the cuttings 

 and often kills them before any shoots appear, or the cuttings may put 

 out sprouts which are later killed by the fungus which gradually travels 

 down the cutting into the bark below the young shoot, thereby girdling 

 the stem and shutting off the food supply from the sprout (PI. 28, D). 



