No. 83]. 368 
on evergreen thorn two (exper. 101 and 102) killed the shoot, three 
(exper. 103 to 105) more or ‘ess checked the growth, while two 
(exper. 116 and 117) showed no effect. The last two experiments 
were begun on August 2, and the others on July 31. The cause of 
the. failures with the thorn both partial and complete is not quite 
plain. The shoots had not reached their full growth, and continued 
to e:cngate after the inoculation. The lateness of the season may 
have had something to do with it, but just what is impossible to say. 
Seven inoculations were made in the twigs of oak-leaved mountain 
ash without results. The dates were July 24 and 29. Owing to 
the earliness with which the mountain ash matures, its wood was al- 
ready solid and practically ripe, and the failure to secure infection 
ought not therefore tobe asurprise. All experiments so far recorded 
were on members of the pear family, having a rather close relationship 
with each other. . 
A few trials were made outside the pear family ; one on stem of 
black raspberry and three on green grapes giving no result, but 
- those on peach proving very interesting. The latter did not, how- 
ever, reproduce the blight, but gave rise to what appeared to be 
genuine gummosis, the further discussion of which will be given 
under that head. 
The variability in the time required for the disease to pass through 
the state of incubation and become outwardly visible was evidently 
due to a number of influences, partly susceptible of statement and 
partly very obscure. The most obvious were the maturity and suc- 
culency of the tissues already mentioned. The influence of the 
vigor of the tree aside from the succulency of. the part inoculated, 
the lateness of the season as a separate factor from the maturity of 
the part experimented with, the weather, particularly the tempera- 
ture and moisture of the air, all have conspired to vary the progress 
of the disease, but no data could be secured. A mechanical difficulty 
presented itself in the case of the apple and quince, for the surface 
of the stems of each, and of the quince fruit, are closely woolly or 
pubescent, and changes in the color of the surface beneath cannot 
be traced readily. In the apple the pubescence about the wound 
often turned brick red, extending sometimes as far along the stem 
as the tissues became diseased, and occasionally aiso showing inside. 
I could not make out what the color, which was usually evanescent, 
was due to, or if it could be produced by other means. The outward 
indication of the disease was not always commensurate with the 
progress within, for in several instances in the fru:t the disease passed 
rapidly to the core but spread iaterally with much slowness, while 
sometimes in the stems it would pass some inches along the inner 
tissues before it showed at the surface. It 1s therefore evident that 
the number of days given in the tables as the time of incubation 
does not represent the same stage of the disease in every case. We 
may, however, say that under favorable circumstances the disease 
will appear in about a week after inoculation. I have now passed 
over the chief features of the experiments establishing the infectious 
