'*:-fii 



v 



Fie. 11. — A germinating ascospore within the apothecium. The dark germ tube 

 has grown out as a young hyaline hypha. Spores were commonly found in this 

 state as late as August 2. Young asci were still forming below. July 1956. (X 1250) 



Alternaria, Chaetomium, Septoria, and Stemphylium. The needles 

 were rotted on the twig, and therefore produced no ascospores of 

 R. pseudotsugae. 



It appears that spores may form in mature apothecia after infected 

 needles fall, but they are not effective as inoculum due to the rapid 

 deterioration of the needles. 



To obtain an accurate appraisal of ascospore dispersal by R. pseu- 

 dotsugae, it was necessary to determine three factors: (1) the time 

 when active liberation of spores first began, (2) the period when 

 spore liberation was at a maximum, and (3) the duration of specu- 

 lation. Such information, along with local meteorological data, was 

 collected at the Camden and Cortland plantations. 



Temperature and relative humidity readings were taken with 

 Fries hygrothermographs. Three of these were calibrated in the 

 laboratory at 100 per cent relative humidity over a two-week period 

 before use in the field. Papers were changed at weekly intervals at the 



34 



