DISEASES. 175 



attack, is too well known to need any learned description. 

 It is well called the blight, for nothing short of scorching 

 by fire can more effectually destroy the life of the tree and 

 blight our hopes of its usefulness. The varied theories 

 and suggestions that have been advanced in attempted ex- 

 planation of this state of things are altogether unsatisfac- 

 torn, so that it may be said we know nothing about the 

 disease, nor whether it be occasioned by frozen sap, by 

 fungous invasion, or by insect attacks, all of which have 

 been set forward as causes of the difficulty. None of . 

 these explanations have been clearly proved, and they 

 seem rather guesses than "established facts in the history 

 of the disease, which breaks out in the midst of the season 

 of growth, and attacks those trees that are in the midst 

 of the most vigorous production of succulent shoots ; but 

 it is not confined to the young wood ; on the contrary, it 

 appears first in the hard bark of limbs, that are two or 

 more years old. This turns brown, becomes desiccated, and 

 thus the circulation is arrested, and the foliage as well as the 

 bark is affected. The outer extremities of the leaves wilt, 

 die, and turn suddenly brown and then black, and often re- 

 main adhering by their petioles for months sad testimoni- 

 als of the destruction caused by the blight. The disease 

 appears to extend in some instances, but it is not proved that 

 there is any poisonous matter generated by a blighted 

 limb that could have entered the circulation, and then have 

 been transmitted to other parts of the tree. The apparent 

 extension of the disease is rather believed to have been 

 the successive development of the trouble from different 

 foci, which had successively invaded so much of the bark 

 as to have more or less completely arrested the flow of 



