536 Journal of Agricultural Research voi. x. no. io 



indicates greater susceptibility of the former under Middle West condi- 

 tions. The disease, so far as found by the writers, has been limited to 

 nurseries. Its prevalence in nurseries is presumably in part due to the 

 favorable conditions prevailing for the dissemination of the fungus in 

 crowded beds. Transit of spores is not only made easy by the short 

 distance between plants but the production of spores is apparently 

 favored by the moisture of the air in the beds. Spore horns are most 

 commonly found in the presumably moister air layer next to the soil 



surface. 



THE PARASITE 



The causal fungus is referred for the present to the genus Phoma. It 

 forms definite pycnidia of a rather unusual type upon both stem and 

 leaves, and no attempt will be made to name it definitely until work now 

 in progress with it can be completed. The pycnidia, which are at first 

 innate, are black, scattered, globose to conical or truncate, rarely more 

 than 0.5 mm. in diameter, and have the somewhat unusual habit of 

 breaking through the epidermis in the early stages of their growth, com- 

 monly before the spore-bearing cavity is differentiated from the rest of 

 the tissue. The cavity subsequently develops in the basal portion of 

 the pycnidial mass, both its upper and lower surfaces being spore bearing. 

 The spores are hyalin, continuous, ellipsoid to oblong, sometimes very 

 shghtly unilateral, guttulate, 7.7 to 12. i by 1.8 to 3.8 jj., commonly 

 9 to 10.5 by 2.5 to 3.0 M (measurements of 50 spores from different 

 sources). The basidia are hyalin, unbranched, filiform, 12 to 15 /x long. 

 The spores are extruded under moist conditions in gelatinous tendrils 

 from I to 3 mm. long, and become brittle on drying (Pi. 61). These 

 emerge through definite ostioles, necessarily long and chimney-like in 

 pycnidia which have a large amount of pseudoparenchyma lying above 

 the spore cavity. While the pycnidia are mostly i -celled, in many 

 of those upon the stem one or more rudimentary partitions arise from 

 the floor of the cavity, this morphological character indicating relation- 

 ship with plurilocular genera. 



The fungus grows well on prune or corn-meal agar, and stains the former 

 a dull orange-red, with the formation in the medium of red crystals 

 superficially like those obtained by Hawkins and Stevens^ from their 

 pigment "B" in Endothia cultures. Fruits are sparingly obtained on 

 prune or corn-meal agar, but more abundently in corn-meal flasks. 

 No ascigerous stage has been so far observed. 



INOCULATION EXPERIMENTS 



In all of the inoculation experiments, 2- or 3- year-old cedar plants were 

 used. The parts to be inoculated were first thoroughly cleaned with a 

 cotton swab and i to 1,000 mercuric-chlorid solution. A wound was 

 then made and mycelium inserted from an agar culture. In all, 11 



1 Hawkins, L. A., and StbvEns, N. E. Endothia pigments. I. In Amer. Jour. Bot., v. 4, no. 6, p. 

 336-353. 1917. 



