MICHIGAN ACADEMY OF SCIENCE. 
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of liquid gelatin, others in tubes of liquid agar, bolli of which were 
allowed to solidify so that a portion of each block was above the 
surface. In about live days white mycelium began to appear on the 
surface of the media. A few days later a portion of this mycelium 
was transferred to sterile bean pods, where it grew quite rapidly and 
in less than one week developed black pustules over the surface of 
the pods. Some of these pustules were mashed in water and examined 
under a microscope and found to lie full of elliptical, hyaline, one- 
celled spores. These black pustules and spores resembled the pycno- 
spores described by Humphrey in 1S91 as developing from ascospores 
growing on culture media. These spores germinate readily in water 
or oilier media, and on agar they produce colonies of white mycelium 
in a few days. 
Hundreds of inoculations have been made in plum and cherry trees 
with these pycnospores and also with the white mycelium growing 
on bean pods, but in no case have the characteristic symptoms of 
black knot resulted. 
To determine whether mycelium of Ploiwir/htia m orb os a would pass 
down from a diseased twig into healthy wood, several scions of dis- 
eased wood bearing knots were whip grafted onto healthy plum trees 
May 10, 1012. In no case did the mycelium pass down from the dis- 
eased scion and infect the healthy stock; but many new knots did 
develop on other limbs of these trees. As these trees were not near 
diseased ones and it was too early in the season for conidia to be 
present the infections must have resulted from the ascospores shot out 
from the knots on the diseased scions used for grafting. 
In the vicinity of Lansing new knots appeared about the first of May 
and by July abundant conidia were being produced. Attempts to 
germinate the conidia in drop cultures were unsuccessful. 
During the month of July, 1912. two hundred and fifty inocula- 
tions were made with conidia in some young plum trees. Up to the 
present time these show no signs of infection; but it is possible that 
the disease may develop during the spring. 
To determine the accuracy of the statement that diseased twigs 
thrown on the ground serve as centers of infection, over one hundred 
diseased twigs were collected here and there throughout an orchard 
of about six hundred plum trees on November 3, 1912. The next 
day samples were taken to the laboratory, sectioned and examined 
with a microscope to determine whether asci and spores had developed 
in the perithecia. In no case was either found. 
The twigs were then tied in a bundle and placed on the ground in 
an exposed position, the same as if they had been cut from the trees 
and dropped on the ground in the orchard. 
December 25, after lying on the ground for almost two months, these 
twigs were again taken to the laboratory, sectioned and examined. 
Some few of the perithecia were still free from spores; but most of 
them were full of asci containing spores that were well developed, 
thus showing that the fungus continues to grow and spores are pro- 
duced after the twigs have been cut from the trees. 
This bundle of twigs was then placed on the ground and left until 
March 12, 1913. when some of the twigs were taken to the laboratory, 
where masses of perithecia were placed on pith blocks in rings, as 
