DETAILED ACCOUNT OF SPECIFIC DISEASES OF PLANTS 497 



Morphology. — On smooth bark, especially in summer, the outer cork 

 layer is raised into numerous little blisters, with slender, yellow, waxy 

 twisted horns emerging from a pore in their apices. A section across 

 each blister reveals a somewhat globose pycnidium surrounded by a 

 scanty loose mass of whitish, or yellowish hyphae, which merge with 

 the tangled hyphae that make up the pycnidial wall. The conidio- 

 phores arise inside the pycnidium, as a dense brush-like fungi and pro- 

 ject into the fruit cavity (Figs. 174 and 176). They range in length 

 from 20 to 40/1. From these conidiophores, spores (pycnospores) are 

 abstricted, and as the cavity is filled with the hyphal stalks, the pyc- 

 nospores are forced out at an opening in the top of the pycnidium in 

 the form of a twisted slimy cord (Figs. 173 and 174). The smooth 

 hyaline pycnospores are held together by a sticky material and they 

 measure 1.28 by 3.56/i in size, and are oblong cylindric with rounded 

 ends sometimes slightly curved. Heald and Gardner^ find that the 

 pycnospores are to a considerable degree resistant to desiccation in 

 soil in the field and that a large number may retain their viability 

 during a period of 2 to 13 days of dry weather (Fig. 177). They 

 found that with indoor desiccation a large number of spores survived 

 two months and that in 5 out of 12 samples not all of the spores had 

 succumbed after three months of drying. The longevity limit varies 

 from 54 to 119 days, the average being 81 days. Studhalter and Rug- 

 gles^ by experimental methods obtained some interesting results as to 

 insects as carriers of the chestnut blight fungus. Tests were made 

 with twenty-one ants in certain laboratory and insectary experiments 

 in which they had been permitted to run over chestnut bark bearing 



1 Heald, F. D. and Gardner, M. W.: Longevity of Pycnospores of the Chestnut 

 Blight Fungus in Soil. Journal Agricultural Research II: 67-75, April 15, 1914. 

 Additional facts in the life history of the chestnut blight fungus are presented 

 in the following: Heald, F. D., and Walton, R. C: The Expulsion of the 

 Ascospores from the Perithecia of Endothia Parasitica (Murr.), Amer. Jour. 

 Bot., 1:449-521, Dec, 1914; Heald, F. D., and Studhalter, R. A.: Seasonal 

 Duration of Ascospore Expulsion of Endothia parasitica. Amer. Journ. Bot., 

 2: 429-448, Nov., 1915; Ibid., The Effect of Continual Desiccation on the Expul- 

 sion of Ascospores of Endothia Parasitica. Mycologia, 7: 126-130; Ibid., Lon- 

 gevity of Pycnospores and Ascospores of Endothia Parasitica under Artificial 

 Conditions. Phytopath, 5:35-44; Stevens, Neil E. : Some Factors Influencing 

 the Prevalence of Endothiagyrosa. Bull. Ton. Bot. Club, 44: 127-144, Mch., 191 7. 



2 Studhalter, R. A. and Ruggles, A. G.: Penna. Dept. of Forestry. Bull. 12, 

 April, 1915. 



32 



