NINTH REPORT. 



NOTES ON THE BLACK KNOT OF PLUM. 



J. B. Dandeno. 



After many unsuccessful attempts to obtain ascospores from the black 

 knot of plum, it was thought worth while to make some special investi- 

 gation into the cause. Sometimes success was met tvit-h, but, for the most 

 part, the material either contained no mature perithecia, or the perithecia 

 were empty. The fact of the matter seems to be thus : It takes about three 

 years (after infection) to produce mature perithecia, and once having been 

 produced, the asci are disseminated, but the old knot remains on the twig, 

 appearing just as it did before the asci had gone. To collect material showing 

 asci and ascospores, the material has to be gathered from the third year's 

 growth. This growth is nearest the apex of the twig, as the fungus works 

 down towards the trunk (figure I). The three years' growth can readily be 

 made out by the appearance of the affected twig (figure 1, 1, 2, 3). The first 

 infection and the first year's growth is shown at 1, the second year's growth 

 at 2, and the third at 3. At 2 and 3 are no perithecia, though in 2 may be 

 seen well rounded knobs similar to those seen on mature knots, but no mature 

 perithecia. 



r--l 



To obtain mature ascospores material had to be collected in April. That 

 collected earlier in the season showed asci as in figure IL Many asci had 

 gelatinous walls, some of which were exceedingly thick (II b). Many of 

 those asci which have such thickened gelatinous walls seem never to produce 

 spores. Those which do, seem to become thin-walled later, appearing as 

 though the material was used up in developing the spore content (figure III). 

 The paraphyses (figure IV) are not very abundant — about one to four of the 



