Cause of Blight on Fruit Trees and Blossoms. 175 



of the sap circulation to give an over supply in rapid growing trees ; and 

 some by electricity or electrical disturbances of the air, when the trees are 

 growing very fast; and others by spores of fungi and bacteria floating in the 

 air and going from tree to tree, etc. 



All of these may cause blight, except perhaps the last named. Although 

 these spores are found in blighted trees it does not prove they cause it, sis 

 they only subsist on dead substances, as far as has been proved. Although 

 it can be inoculated on healthy trees by insertion, it does not prove that it 

 is contagious. Still it may be so, but we doubt it. As the cellular structure 

 of the cambium layer, or the conversion of the water as drawn up by the 

 succulent roots and conveyed through the cell tubes up in the sap wood or 

 ducts, provided for in the last year's new cambium layer, under the bark on 

 the body of the tree to the new shoots, to be converted into sap and to build 

 the leaf structure, or cell after cell, and the action of the sun, warmth and 

 air act upon the leaf or evaporate the water or crude sap (as Mr. J. W. Eob- 

 son has remarked in his paper on the circulation of the sap in trees and 

 plants), to tit it for distribution and dissemination on its mission to facilitate 

 the growth of the tree or fruit. 



The action of this is interrupted by some cause in its working up of this 

 water (or crude sap), or in converting it to the proper consistency of food 

 the tree requires at a particular sttige of its growth. Excessive heat or sun 

 scald will cause this. On a healthy and fast growing tree it will require froin 

 W to 98 degrees of heat to interfere with the action converting this food into 

 a sort of jelly (or thickening up of sap), which can not disseminate, hence 

 a stoppage in the cell structure, and fermentation commences (here it is, 

 where bacteria commences to work and, as soon as decay is visible, fungi) in 

 the ne vv leaves. 



But on a tree not perfectly healthy, such as those injured by deficiency in 

 foliage, either caused by insects, mildew, or a hailstorm, or an early frost in 

 the fall, or by late growth, whereby the ripening-up process was interrupted, 

 the new wood or cambium layer is watery and not ripe, the severe cold in 

 winter will atlect it more or less, and rupture it; 90 to 94 degrees will have 

 the same effect. 



To illustrate: A few years ago we experimented on apple blossoms, and 

 observed that the petals on the flowers wilted during the day when the trees 

 were about in full bloom, but before they would naturally drop off. (We had 

 at the time a southwest wind, and the thermometer ranging from 90 to 96 in 

 the shade.) They did not recover or straighten out during the nights, and 

 we found on close examination they were scalded or burned, as it were, and 

 in a few days looked like fire had run through them, from this blight. 



Trees that had no blossoms open, or had no blossom-buds to open, were 

 not in the least affected, neither then nor during the summer — only those 

 that were all out in full bloom on those three hot days perished. 



It looked to me, then, that so much surface of so much bloom and leaves 

 were not supplied fast enough with sap, to allay the evaporation going on 

 during the time, to keep the petals from wilting or scorching. 



