Pathogenicity of the Chestnut Bark Disease 47 



Development of Stromata, Pycnidia, and Perithecia. 



The first attempt of the fungus to fructify results in the 

 formation of a stroma a compact mass of mycelial hyphae hav- 

 ing a pseudo-parenchymatous structure in which the fruiting 

 bodies are embedded. The pycnidium is a chamber with rela- 

 tively thin convoluted walls at the bottom and around the sides 

 of which are many short stalks closely pressed together from the 

 ends of which the conidia or summer spores are constricted. After 

 one spore is abstricted another one is successively formed be- 

 neath it. These spores are covered with a mucilaginous sub- 

 stance which holds them together. The mass of spores thus held 

 together and continually pushed out from the bottom forms the 

 "spore horn". The longest "spore horn" collected by the writer 

 measured 2]/ 2 inches in length and some were found which were 

 over one-eighth of an inch in diameter. The fact that there is 

 no definite shape to the ''spore horn" confirms the theory that 

 there is no regular ostiole in the pycnidium but that the spores 

 simply break out at the point where the wall is the weakest. While 

 pycnidia were found throughout the year, they were especially 

 abundant during the summer months. 



The perithecia small flask-shaped fruiting bodies of the 

 winter stage are formed in the same stromata in which the pyc- 

 nidia are produced. The spores of this stage are borne together 

 in groups of eight in transparent sacs or asci. These asci stand 

 out vertically from the inside walls of the perithecium. About 

 July first it was found, on sectioning material, that the perithecia 

 were beginning to develop in the same pustules with the pycnidia. 

 The pustules containing pycnidia and perithecia varied in size 

 from 3 to 4 mm. The number of perithecia in each pustule var- 

 ied from 3 to over 30. Material carefully examined on July 6 

 showed that the necks of the perithecia were apparently just push- 

 ing above the stroma. The old stromata were a cinnamon red 

 color from age while the newly formed necks were bright yellow. 

 These observations indicated that the ascospore stage was then 

 being matured. 



If a piece of bark infected with mycelium is exposed to cold 

 or thoroughly dried for some time so that the mycelium has ceased 

 to grow, the fungus on being exposed to warmth and moisture 

 will often produce perithecia. Bark permeated with the mycelium, 

 which had not been exposed to cold or thoroughly dried, on being 

 placed in saturated air at a temperature of from 19 to 24 C. 

 produced conidiospores abundantly. A five year old branch of 

 chestnut bearing a canker caused by the fungus had, under sim- 



