142 
FIFTEENTH REPORT. 
SOME NOTES ON THE BLACK KNOT OF PLUMS AND CHERRIES. 
BY J. A. MCCLINTOCK. 
Investigations were begun on the life history of Ploicrightia morbosa 
in the fall of 1011. The first step was to determine at what time the 
ascospores appeared. These observations have shown that the time 
of year when ascospores develop varies somewhat. For example, in 
1011, well developed spores were found November 1G; while in 1012, 
knots from the same tree failed to develop these spores until early 
in December, or about fifteen days later than in 1011. 
During the season of 1011 and 1012 constant attempts were made 
to germinate ascospores in drop-cultures, using a great variety of 
media. Late in April some of the spores in one culture, with tap- 
water as a medium, did send out short germ tubes, but never pro- 
duced mvcelium. With this exception all the attempts were unsuccess- 
ful. 
To avoid the constant bacterial contamination which occurred when 
perithecia were mashed up and put directly into drop culture, at- 
tempts were made this winter to get the ascospores free from con- 
tamination at the start. After several unsuccessful attempts a prac- 
tical method was devised as follows: A glass ring was sealed to a 
slide: then a small block of pith was cemented to the slide in the 
center of the ring and moistened with tap water. On top of this 
block was placed a small mass of perithecia directly from a knot; 
then a sterile cover glass was sealed down over the top of the ring. 
The moisture from the pith block soon passed up as vapor and con- 
densed on the dry, sterile cover glass in small drops. Such a culture 
was then set away in a warm place over night, and the next morning 
when examined under a microscope the drops of water on the cover 
glass were found to he abundantly stocked with ascospores, thus 
showing that under warm, moist conditions the asci are able to shoot 
their spores. 
By varying the distance from the perithecia to the cover glass it 
was found that some spores were shot more than one centimeter directly 
upward from the asci ; but a far greater number were found on the 
cover glass when it was one-half centimeter or less from the surface 
of the perithecia. 
Spores collected in this way germinated within forty-eight hours; 
the germ tubes being pushed out either from the tip of the larger cell 
or from the side of this cell near the septum. In no case were germ 
tubes pushed out from the smaller cell of the spore. 
On failure in 1011 to get cultures by germinating ascospores, at- 
tempts were made to get cultures from the diseased wood by the fol- 
lowing method: Small blocks of diseased wood were cut from plum 
twigs, just below the point where the knots had formed. These blocks 
were disinfected externally in 05% alcohol and HgCL. Then the bark 
was removed with sterile tools and some of the blocks placed in tubes 
