OBSERVATIONS ON FOREST TREE RUSTS 
James R. Weir and Ernest E. Hubert 
The undertaking of the checking by cultural methods of various 
forest-tree rusts occurring in the Northwest has established several 
host relationships previously held doubtful. The recent works of 
Eraser^ and Ludwig^ have aided in the clearing of some of the problems 
concerned. Eraser's results with species of Uredinopsis on ferns and 
the final conclusion to the effect that the five species of Uredinopsis 
used in his experiments have their aecial stage on Abies halsamea is an 
important contribution toward a clearer understanding of the inter- 
esting group of rusts occurring on ferns. The five species with which 
Eraser worked are Uredinopsis struthiopteridis Stormer, U. osmundae 
Magn., U. atkinsonii Magn., U. mirabilis Magn., and U. phegopteridis 
Arth., and a study of the microscopical characters reveals no great 
differences between them. Eraser^ in his last article came to the 
conclusion that all of the five species with which he had been working 
were identical with the exception of U. mirabilis and considered this 
one different on account of the fact that positive results with aecio- 
spores from Abies balsamea were secured on Onoclea sensibilis only. 
In a recent communication received from Eraser, March 27, 1916, he 
states that Arthur examined all the field collections of Peridermium 
balsameum Pk. and cultures and came to the conclusion that there are 
no morphological differences in the aecial stages produced on Abies 
balsamea by inoculations of the five species of Uredinopsis. A close 
comparison of the spore measurements and lengths of beaks of the five 
species as published by Arthur^ show no great differences in size from 
what might be expected as a result of the influences of the various 
^ Eraser, W, P. (a) Cultures of Heteroecious Rusts, Mycologia, 4: 175. 1912. 
(6) Further Cultures of Heteroecious Rusts. Mycologia, 5: 233. 1913. 
(t) Notes on Uredinopsis mirabilis and Other Rusts. Mycologia 6: 25. 1914. 
2 Ludwig, C. A. Notes on Some North American Rusts with Caeoma-like Sori. 
Phytopathology 5: 273, 1915. 
3 Eraser, W. P. Notes on Uredinopsis mirabilis and Other Rusts. Mycologia 
6: 25. 1914. 
^Arthur, J. S. Uredinales, N. Amer. Elora 7: 115. 1907. 
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