Blister Canker 
25 
The greatest difficulty lay in obtaining a desirable stain. 
Several were tried with unsatisfactory results. The Pianese 
stain used by Vaughan^i was promising but required a long 
time to stain the hyphae and when this was accomplished the 
staining of the cells was so dense that the hyphae were ob- 
scured. At the suggestion of Doctor McCormick the formula 
was changed as well as the subsequent treatment of the sec- 
tions with very gratifying results. The modified formula was : 
Malachite green 0.50 gm. 
Acid fuchsin._ _ _ _ _ _ 0.50 gm. 
Martius gelb 0.02 gm. 
Water (distilled) _ 150.00 cc. 
Alcohol (95 per cent) _ _ _ 50.00 cc. 
The sections were cleared in carbolturpentine, washed in 
95 per cent and absolute alcohol and stored in xylol. Mount- 
ings were in balsam. By this method the cells were stained 
green and the hyphae a deep pink. Staining required only two 
to five minutes. 
By comparing the discoloration of inoculations where mi- 
croscopic examination revealed the hyphae invading the tis- 
sues with that made by incisions where no inoculum was in- 
serted, it was found extremely easy in the majority of cases to 
recognize infections. Therefore, after more than 200 inocula- 
tions had been examined to the extreme limits of the invaded 
tissues, the presence of the characteristic discoloration was 
taken as an indication of the presence of infection, except in 
doubtful cases when the microscope was employed. 
No inoculations were made from these artificial infec- 
tions.* The fact that characteristic stromata and conidia 
were produced from infections caused by each of the inocula 
used was considered ample proof as to the identity of the infec- 
tions. No ascospores have yet been produced on any of the 
cankers from artificial infection. 
While examining inoculations for infection, it was ob- 
served that in a number of cases the infection extended to all 
parts of the tree. This aroused a suspicion that the tree might 
have been infected at some previous time in spite of the pre- 
cautions taken to select sound trees, especially as several 
places were found where infection might have occurred, such 
as frost cracks in the trunk and old pruning wounds. This 
led to the examination of a large number of trees which 
showed no visible signs of canker. The results were discour- 
*Since preparing- this manuscript the author has isolated the causal 
fungus from some of these artificial infections and made new inoculations 
which have produced typical cankers. 
