342 PLAIN AISTD PLEASANT TALK 



or insect-track has been detected, except those which have 

 attacked the tree in consequence of the blight. 



To be sure, we oan find bugs, black, brown, green and 

 grey, but the mere presence of an insect is nothing, though 

 with many, it seems enough, when a tree is blighted, if a 

 bug is found on it, to determine the parentage of the mis- 

 chief. Nor do the published accounts of insects, found on 

 blighted trees, increase our respect for this theory. The 

 observations seem to have been not thorough enough, and 

 not carefully made, and the reasonings even less philo- 

 sophical. Men have searched for a theory rather than for 

 the mere facts in the case. But by far the greatest num- 

 ber of those who write, give no evidence of relying upon 

 any observations which they have themselves made, but go 

 back perpetually to the old precedents, Mr. Lowell and 

 Professor Peck, without being at any pains to verify them. 

 Has Dr. Kirtland ever found the scolytus pyri ? Has he 

 ever, in time of extensive bhght, found it under such cir- 

 cuTnstances as to satisfy his mind that it was the real cause 

 of fire-blight ? or does he rest satisfied that blight is occa- 

 sioned by an insect simply because so it is set down in good 

 books ? The canker may be mistaken for blight by those 

 who have not been acquainted with either ; but surely, no 

 one who has ever attentively examined one real case of fire- 

 blight would ever mistake it for anything else, or anything 

 else for it. 



The insect theory we regard as wholly untenable except 

 for special, local, peculiar ravages which are not properly 

 blights. The blight is a disease of the circulation. It 

 aficcts every tissue of the plant. It is not a disease fi-om 

 exhaustion of sap by the suction of aphides, as Dr. Mosher, 

 of Cincinnati, supposed, for the trees have a plethora rather 

 than scarcity of sap ; it lacerates the sap-vessels, bursts the 

 bark, flows down the branches, and dries in globules upon 

 the trunk. On cutting the tree, if the blight is yet new, 

 the texture of the alburnum will be found to resemble what 



