• 



Q 



Fig. 15. — Ascospores adhering to the surface of a young needle. The hyaline 

 ends of the spores have partially disintegrated. The hlack cell of the ascospore 

 on the left shows a very young germ tube apparently about to penetrate through 

 the cuticle. (X 800) 



Studies on pathogenicity, mode of infection, and physiology of 

 R. pseudotsngae would be facilitated if it were possible to glow the 

 fungus on artificial media. Subsequent investigation of varietal 

 reaction of host trees and of the suggested heterothallism of the 

 pathogen (70) would also be possible. All attempts to culture 

 R. pseudotsngae failed, thus tending to substantiate Van Vloten's 

 (63) suggestion that the fungus is an obligate parasite. However, if 

 Rhabdogloeum hypophyllum is the imperfect stage of Rhabdocline 

 psendotsugae, the obligate nature of the latter might still be ques- 

 tioned, since the former has been successfully cultured (15, 68) and 

 conidia were produced. 



To obtain more information on the method and site of needle 

 penetration, fresh apothecia were scraped from infected needles and 

 placed in sterile distilled water. After two hours this inoculum was 

 applied to the tender needles of newly expanded shoots of potted 

 trees in the greenhouse. After 6, 12, and 24 hours, needles were 

 coated with egg white (applied by means of an atomizer) in an 

 attempt to hold spores onto the surface of the needle during subse- 

 quent preparation for sectioning. Young needles were excised from 

 the twig, killed and fixed in formalin-acetic acid-alcohol, dehydrated 

 using Johansen's (24) tertiary butyl-ethyl alcohol series, and em- 



38 



