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chiefly developed, ramifying between the cells and sending haustoria into 
the cells; from the cortex it extends into the woody portion by way of the 
medullary ray cells. The cortical parenchyma cells contain a few chloro- 
phyll and starch grains. The starch is most abundantly found in the 
older portions of the “witches’ broom”. The septate mycelium is un- 
doubtedly perennial in the buds, although Rees makes a contrary state- 
ment in regard to P. ahietinum. 
Genetic Connection. Elsewhere reference has been made to the results 
of infection experiments of DeBary, from which it was shown that Peri- 
dermium abietinum is connected with Chrysomyxa rhododendri. As noted 
in the paper by Farlow the Chrysomyxa was not found on Rhododendron. 
Chrysomyxa ledi on Ledum is probably connected with P. abietinum in 
the vicinity of the P. abietinum in the White Mountains. 
In the Uintah Mountains and Iviedicine Bow Mountains where the 
WTiter has observed this Peridermium neither of these Ericaceous plants 
occurs. The only other Ericaceous plants in these regions are several 
species of Pyrola on w’-hich a Credo has been found; Kalmia glauca usually 
free from fungi, and Vaccinium of w'-hich there are several species, the 
most common being V. caespitosum. The distribution of Vaccinium and 
Kalmia is coetaneous with the Picea engelmanni. The Vaccinium is 
commonly affected with Calyptospora goeppertiana whose aecidium is 
Peridermium columnare a fungus which has not been observed by us in 
the Rocky Mountains, though if abundant it should be easily recognized. 
It seems most probable that our Peridermium aiffers from the P. abieti- 
num of Europe and of the eastern states, although resembling it in mor- 
phological characters. 
In the Big Horn country Ledum glandulosum may be found and Prof. 
A. NelsoiP reports Chrysomyxa ledi on it in the Yellowstone National 
Park, but this hos;: is not abundant in the Uintah Mountains. Since writ- 
ing the above Chrysomyxa ledi has been found in these mountains in 
close proximity to the Peridermium coloradense. If cultural experiments 
show that this form is distinct from the European P. abietinum the name 
of P. coloradense may be retained. Cultural experiments will no doubt 
show that it is distinct as it appears to be structurally. 
Exoasceae 
No commercial trees of the region under discussion are affected by the 
genera of the group Exoasci, although smaller ones like Betula occiden- 
talis, Prunus demissa, P. pennsylvanica and Quescus gunnisoni are 
attacked by fungi of this group, which are at times quite destructive. 
Many of the species of the genus Exoascus produce curious malformations 
caused by the perennial mycelium of the parasite, living in the ends of 
twigs and stimulating the stems to put out tufts or small branches, which 
result in the formation of the so-called “witches’ broom” or hexenbesen 
of the Germans. 
1. The Cryptogams of Wyoming. Ann. Eep. Agrl. Exp. Sta. 10; 30, No. 
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