71 
vast numbers. Mist or fogs are not so apt to free the conidia,* but 
these are favorable to germination. 
It is, perhaps, too early to consider preventive measures, as thus far 
no experiments, so far as I am aware, have been conducted to this end. 
There are one or two suggestions, however, which it may be well to make 
in view of the observations in the field and laboratory. 
(1) Let all fallen foliage be gathered from beneath infested trees and 
burned. 
(2) Have the earth beneath the infested trees carefully and com¬ 
pletely turned under, the deeper the better. 
It is important that spray applications of known fungicides should 
be made with thoroughness, both to trees and soil, to the latter after 
the fall of the foliage. In applying sprays to the tree it should be re¬ 
membered that a great majority of the spores of Cercospora eircumscissa 
are produced on the under surface of the leaves and branches. 
OBSERVATIONS ON THE PARASITE. 
The microscopical study of Cercospora eircumscissa reveals much 
variation in form and habit. There are presented, by means of the cam¬ 
era lucida, some of the variations observed in the production and form 
of its conidia. . There are also given numerous figures showing the 
characteristic but greatly varying habit of germination. (Plate xii.) 
The conidia vary both in length and form. They are from 1 to 6 or 
7 celled; mostly 2 to 5 celled. The distal one-fourth to one-half is 
usually reduced in transverse diameter and the cells are longer than 
those of the proximal portion. Toward the base of the conidium the 
cells are often somewhat distended at the equator. This gives the 
basal half a slightly undulating outline from septum to septum. The 
width of the distal end varies between 3 p and 4 p, while the greatest 
breadth taken toward the base varies between 4 p and 6 p. The basal 
cell contracts rather abruptly toward the end, to a transverse diameter 
about equal that of the distal end of the conidium. The length of the 
conidium is found to vary according to certain favorable or unfavorable 
conditions of growth. The most common variation is between 22 p 
* The formation and attachment of the conidia are examined with difficulty in 
water. When a section hearing conidia is placed in water the spores become free. 
This may be avoided by placing the sections upon the slide nearly dry and afterwards 
moistening them gradually by breathing beneath the cover glass. The condensed 
vapors soon gather about the conidia and answer the purpose of a water mount in 
the transmission of light rays, while the conidia remain attached to their conidio- 
pliores. Glycerine or water may afterwards be run under the cover glass with much 
greater safety. When profile views of attached .conidia are desired it is convenient 
to cement the back of the spore-bearing leaf tissue to a section of cork 2 millime¬ 
ters in thickness. When dry the cork' serves as a firm support in sectioning; and, 
owing to its thickness, it insures that the section shall lie so that the desired pro¬ 
file view is obtained. The cork is removed by running water over the sections and 
then teasing them with a fine brush. 
