Heald; Chestnut Blight Fungus 
275 
The medium found most suitable for this work was 3 per cent, 
dextrose agar, plus 10, made according to the standard bac- 
teriological formula. The comparative rate of growth from asco- 
spores and pycnospores was first tested in this medium by means 
of hanging-block cultures. The pycnospores used were obtained 
from spore-horns grown in damp chambers in the laboratory. 
The ascospores were obtained by placing flamed object slides 
over moistened bark bearing perithecial pustules and collecting 
the expelled spores. In making the pycnospore cultures a drop 
of sterile bouillon was placed on a flamed slide and a small spore- 
horn added to it. One or more dilutions were made from this to 
other drops of sterile bouillon and a short streak was made from 
the final dilution upon the surface of the cover glass, after which 
the streak was covered with melted agar cooled to 42° C. In 
making the ascospore cultures a drop of sterile bouillon was 
placed over a spore print on a slide. Dilutions were made from 
this to a second slide, and the planting made directly from the 
spore dilution. 
By these methods there was never any trouble in securing pure 
cultures in the hanging drop cells. 
Germination of Pycnospores and Ascospores 
During the first part of the germination period the pycnospore 
increases in size until it is oval or oblong in form and slightly in 
excess of the diameter of the germ tube that is to be produced 
(plate 98, figs. 1-3). A hypha begins to grow out from one end 
of the spore and this is generally followed later by one from the 
opposite end so that at temperatures from 22° to 25° C., only an 
unbranched linear aggregate has been produced at the end of 24 
hours. During the next 24 hours, however, branching generally 
begins, the first branch originating a little beyond the limits of the 
spore, thus producing a distinct Y-type of growth (plate 98, 
figs. 4-6). 
Each cell of an ascospore generally gives rise directly to at 
least one vigorous hypha, but occasionally one cell fails to germi- 
nate. In many spores each cell gives rise to a lateral hypha a 
little later. In case a lateral hypha is not formed directly from 
