

1 



IAY 



5 



JUNE 



15 



JULY 

 15 







90 





a KV 



A 





Maximum daily 



80 



A 



.A/ \a/i a , 



1/1 A ^n > 



^ 



temperature 



(degrees 

 Fahrenheit) 



70 

 60 



jo 



lA- 



n/ v ^wy 



M/VA/ 



V 



Average weekly 



60 











spore cast 



40 











(per 1.67 sq. ■>».) 



20 

 













90 







A 





Maximum daily 



80 



A ft 



/i »/\ / 



1 A , 





relative hustldity 



70 



IAa 



X /AaA A(v 



PUV 



\ 



(per cent) 



60 

 50 



^J 



vy v/vi / v v 



v w v 



\n 



Fig. 13. — Ascospore discharge at the Camden plantation, 1956. Maximum tem- 

 perature and relative humidity are plotted on a daily basis. The center graph 

 shows the number of ascospores deposited, per 1.67 sq. mm. of slide, per week. 

 Each weekly plot is the average of 12 slides. 



shape, comparatively large size, and the cell differences in the asco- 

 spores of R. pseudotsugae made them easy to identify accurately. 

 An index of spore discharge was based on the number of ascospores 

 of R. pseudotsugae counted under low power on a slide area of 

 1.67 sq. mm. 



The results from the spore-dispersal study are presented by graphs 

 relating ascospore discharge to temperature and relative humidity 

 (Figs. 13 and 14). 



Ascospores were first identified on slides from Camden on May 29 

 (Fig. 13). The gradual warming of the area in late May apparently 

 initiated ascospore discharge, but a sharp increase in relative humid- 

 ity coincident with a rapid increase in the number of spores trapped, 

 suggests that moisture is more important in sporulation of R. pseu- 

 dotsugae than is temperature. Ascospore dissemination reached a 

 peak at Camden during the week ending June 26, then decreased 

 gradually until the week ending July 17. At that time a renewed 



36 



