ately low relative humidity, and it is doubtful that 

 pine infection could have resulted. In autumn, though 

 longer moist periods associated with frontal storms 

 are again more common, temperatures are probably 

 too cold for basidiospore casting. Thus it seems that 

 weather conditions that could lead to abundant pine 

 infection are rare in the Rocky Mountain States. 



Tissue Susceptibility 



By the time teUa are present on comandra, 

 stems of lodgepole pine have finished elongation and 

 are no longer succulent. This has been taken to indi- 

 cate that pine infection occurs through needles rather 

 than directly in stems. Whereas results from experi- 

 mental infection of lodgepole pine and from phono- 

 logical data indicate that current-year and 1 -year-old 

 shoots are probably more susceptible, four young 

 infections found in Teton National Forest in 1966 

 support a different view. These infections, like those 

 artificially induced, were on needle-bearing stems and 

 had produced about the same degree of swelling; 

 pycnia were exuding apparently for the first time. If 

 we assume that the young trees were infected only 1 

 or 2 years previously, like the artificially infected 

 seedlings in a similar stage of development, we can 

 conclude that two infections entered 2- or 3-year-old 

 shoots, one a 3- or 4-year-old shoot, and one a 4- or 

 5-year-old shoot. This apparent contradiction of evi- 

 dence from my pine infection trials stresses the need 

 for additional information on susceptibility of tissues. 



Seasonal Spore Viability 



Studies were designed to determine viability 

 of spores collected throughout a growing season. Via- 

 bUity at 18 ±0.5 C. was determined with samples 

 collected from fruiting structures once a week. Aecio- 

 spores were tested on collodion films on distilled 

 water and urediniospores and basidiospores on 2 per- 

 cent water agar; teliospore viabihty (measured by 

 numbers of basidiospores cast from whole teUa) was 

 determined in moist chambers over 2 percent water 

 agar at pH 2. Telia were incubated 72 hours and other 

 spores 24 hours. At least 200 aeciospores or uredinio- 

 spores were examined in each test for percent germi- 

 nation, and 20 each for length of germ tubes. Percent 

 germination multiplied by mean germ tube length 

 gave an index of germination (trends of both percent 

 and lengths were similar). 



z '0 



2 5 



Shasta urad 



-300 X 

 200 



BASIDIOSPORES 



31 10 20 30 10 20 31 10 20 31 10 20 30 10 20 

 JUNE JULY AUGUST SEPTEMBER 



Figure 2 3. -Prevalence of C. comandrae fruiting 

 structures and corresponding viability in 

 Fish Haven plot 1964. In bottom graph, 

 curves are shown for germination by for- 

 mation of a germ tube (primary) or by 

 production of another basidiospore 

 (secondary). 



10 20 30 10 20 31 10 20 31 10 20 30 10 

 JUNE JULY AUGUST SEPTEMBER 



Figure 24. --Prevalence of C. comandrae fruiting 

 structures and conesponding viability in 

 Beaver Mountain plot 1965. Since germi- 

 nation of basidiospores during this year 

 was entirely by formation of germ tubes, 

 only one curve is shown. 



23 



