24 hours (table 3). On the basis of both percent 

 germination and length of germ tubes at 24 hours, 

 germination seemed best between 13° and 23° C. and 

 poor at 3° C. and at 28° C. or higher (fig. 6). Like 

 aeciospores, urediniospores germinated equally well 

 in low light (such as might occur on cloudy days) and 

 in darkness, but did not germinate in bright sunlight. 



Urediniospores were also deposited on 

 comandra shoots in the Cache National Forest plot 

 mentioned earlier. In two trials in which 10 days of 

 conditions unfavorable for infection followed deposi- 

 tion, no shoots became infected. However, uredinia 

 developed on shoots in two trials in which only 6 

 days of unfavorable conditions followed spore deposi- 

 tion. Thus, even during short dry spells in a warm 

 summer, dissemination of urediniospores can lead to 

 infection of comandra. 



TELIOSPORES 



TeHa contain up to several hundred telio- 

 spores bound firmly together as hairlike projections 

 on comandra leaves (fig. 7) and stems. As soon as 

 conditions are favorable, each teliospore may germi- 

 nate in place and form a basidium and (usually) four 

 basidiospores that are disseminated by air (Hedgcock 

 and Long 1915). This process, referred to here as 

 basidiospore casting, may lead to the dispersal of 

 many hundred airborne basidiospores from each 

 telium. Thus teHa and tehospores are not themselves 

 disseminated, but produce the wind-disseminated 

 spores that infect pines. 



Effects of Humidity on Germination 



To determine whether saturated air is neces- 

 sary for germination of tehospores, telia were tested 

 in petri-plate chambers in which humidity was con- 

 trolled by saturated salt solutions or distilled water 

 (table 4). Excised teha from comandra leaves were 

 stuck by their basal ends to petrolatum on the inside 

 of petri-plate covers, and glass shdes were placed 

 beneath the teUa to catch dispersed basidiospores. 

 Plates were sealed and incubated in darkness at 

 20° ±0.1° C. for 24 hours. Slides were then examined 

 microscopically for the presence of basidiospores. 

 They were found on slides in chambers in which rela- 

 tive humidity was 100 percent, but not on shdes in 

 chambers in which humidity was 98 percent or lower 

 (table 4). 



Figure 5 .--Germinated urediniospore after 



24-hour incubation (X 43?}. 



TEMPERATURE (D.gr... Calsiut) 



Figure 6. -Germination of urediniospores at sev- 

 eral temperatures after 24-hour incu- 

 bation. The darker lines represent means 

 of four individual trials. 



6 



