16 BULLETIN 247, U. S. DEPARTMENT OF AGRICULTURE. 



the center of infection or, vice versa, may spread from the point of 

 infection on a limb to that part of the trunk adjacent to the diseased 

 area on the limb. In this it resembles P. filamentosum (5) and the 

 fusiform type of P. cerebrum (P. fusiforme) (7, p. 248). Such in- 

 stances in the case of both P. pyriforme and P . filamentosum on Pinus 

 ponderosa have been observed by the senior writer in Colorado and 

 Wyoming and noted by Spaulding (11, p. 28, 34) in the case of Peri- 

 dermium strobi on white pines in the northeastern United States. 



EFFECT OF THE UREDINIAL AND TELIAL FORMS ON COMANDRA PLANTS. 



The effect of the uredinial and telial forms of the fungus, Cronartium 

 pyriforme, on Comandra plants can not be separated into two distinct 

 sets of symptoms, since the two forms are produced on the same 

 area of tissue, the one following the other in a few days. Both the 

 uredinia or the telia may occur on either surface of the leaves, as 

 well as on the younger portions of the stems, and occasionally on the 

 floral parts. 1 In badly infected plants there is a decided shortening 

 of both the stems and the leaves in their growth, so much so as to 

 change the entire aspect of the plants. This is usually accompanied 

 by a slight chlorosis of the leaves. Where the infection is slight, the 

 diseased spots on the leaves are usually a lighter green color than the 

 uninfected portions. Late in the growing season the reverse colora- 

 tion sometimes takes place, and the chlorophyll is retained longest 

 in light-green areas in the leaves where the mycelium of the fungus 

 is found, even after the remainder of the leaf has become yellow from 

 fall coloration. 



In badly infected Comandra plants defoliation takes place prema- 

 turely; that is, before drought, frost, or cold weather bring it about. 

 No data have been obtained as to the final effect of the rust on 

 Comandra plants. The effect, however, is decidedly stunting, and 

 plants infected badly for several seasons would undoubtedly be killed. 



ERADICATION AND CONTROL OF THE FUNGUS. 



One of the most serious facts in connection with the prevalence of 

 Peridermium pyriforme in some portions of the western United States 

 is the danger of introducing it into localities now free from it through 

 the shipment of trees in the work of artificial reforestation. For this 

 purpose nursery stock is often shipped long distances. The forest 

 nursery if situated in mountain regions is apt to be in a locality where 

 Comandra plants are common. Since these serve as host plants for 

 both the uredinial and telial forms of the fungus, their presence may 

 lead directly to the infection of the young pines in the nursery and 

 indirectly to the infection of localities hitherto free from the disease. 



i IB Comandra pallida this is the case. In Comandra umbellata the uredinia and telia are found uniformly 

 on the under surface of the leaves. 



