121 
Certain Fungi Parasitic on Plants. 
modes, the asci containing the true sporidia will escape, and fre- 
quently the sporidia will be seen in profusion on the glass. I have 
counted as many as ten sporidia in one ascus. When the peri- 
thecium is very pliable, and the interior mass of asci well matured, 
it may be removed entirely by pressure, as represented at A. A 
power of about 600 diameters is necessary to see it properly. 
An ascus measures about T tto <jfh of an inch in diameter, and is 
about seven times its diameter in' length. 
If an ascus is treated with an alcoholic solution of iodine, con- 
taining a few drops of nitric acid, its nitrogenous matter becomes 
stained of a dark amber while the sporidia retain their natural 
colour. The asci will frequently exhibit, when treated with acids 
and alkalies, an expanded membrane of very delicate texture and 
quite transparent, as exhibited at B and C, Plate XCYI. 
The true cause of this disease is unknown at present. My 
future investigations will be principally confined to its mode of 
propagation. Investigations of this character lose much of their 
value when they are confined to the microscope and laboratory. 
Districts affected with the dreaded pest should be visited, and the 
roots of the trees and their branches examined, that the investigator 
may become acquainted with all the stages of growth of the fungus, 
and. thus ascertain how the disease is propagated. 
(2) The fungus Erysiphe Tuckeri. 
On the 15th of May last, one of the foreign grape-vines of 
the experimental grapery of the Department of Agriculture was 
found to be affected with the fungus called Oidium Tuckeri. It 
first appeared on the leaves, then on the green branches, and finally 
on the fruit. 
I determined to take advantage of its presence to make further 
investigations in reference to its habits. I secured on a glass slide 
a few of its Oidium spores, placed them in a clean glass jar containing 
a little water, excluded the atmosphere by a ground-glass stopper, 
and subjected the jar to a temperature of about 75° Fahr. during 
the investigations. On the second day the spores were examined, 
when it was found that many of them had germinated. 
1, group A, Plate XCVII., represents the Oidium. I think that 
the spores in this case are thrown out from the peduncle * in the 
same manner as soap-bubbles from a pipe. I have never seen a case 
of an Oidium spore having a small spore attached to it as if in the 
act of reproducing a facsimile of itself, as is so frequently observed 
in the spores of the common yeast-plant ( Torula cerevisise). The 
Oidium spores germinated and threw out branches as shown in the 
drawings 2, 3, and 4. The protruding branch of' spore 2 differs in 
* The stem or stalk that supports the flower aud fruit of a plant. 
