62 Nebraska Agricultural Exp. Station, Research Bui. 12 
than new tissues were being added on the outside. When the 
growth of the trees was materially checked the fungus gained 
very rapidly often killing the tree. This explains why so many 
Ben Davis trees died during and soon after the severe drouth 
of 1913. The trees were already infected and were checked 
by the drouth to such an extent that the fungus was able to 
invade the tissues very rapidly. Jonathan, Winesap, and 
many other varieties suffered to a much less extent. In these 
varieties the fungus was found to progress little if any faster 
after active tissues were encountered than new tissues were 
added when the trees were in a normal condition. Hence even 
when checked by the drouth these varieties still offered a 
great deal of resistance to its advance. 
METHODS OF PREVENTING INFECTION 
All accumulated data and observations indicate that 
methods of control for blister canker must be preventive 
rather than curative. 
The importance of avoiding wounds of all kinds to any 
parts of the tree has already been emphasized, as well as the 
necessity of keeping the tree in a moderately vigorous state of 
growth. The protection of all wounds from infection is of the 
utmost importance. This may be done by eliminating the 
source of infection by preventing the formation of spores, or 
inhibiting them in some manner, and by using disinfectants 
and adhesive dressings for the wounds. 
It was noticed in the laboratory that the stromata absorb 
water very readily, and that a considerable amount was taken 
up before the spores were expelled. Copper sulphate and lime 
sulphur were then used to ascertain if such materials would 
inhibit spore germination. The different materials in solution 
were absorbed readily and the beneficial results were found to 
be twofold. The quantities of spores expelled were noticeably 
less when either copper sulphate or lime sulphur was used 
than when water was used. It was also found that a high per- 
centage of the spores did not germinate. The difference was 
most striking when copper sulphate was employed. When 
lime sulphur was used about 3 per cent to 5 per cent of the 
spores germinated and a few produced normal mycelium. 
When copper sulphate was used 1 per cent to 3 per cent ger- 
minated but in no case was normal growth obtained. The 
hyphae rarely reached the branching stage but after they at- 
tained a length of about 1 mm. remained stationary for a time 
and then disintegrated. 
