INDIANA HOBTICULTTJKAL SOCIETY.' 413 



On dissecting tlie branch the wood is of a dirty, brownish yellow 

 color; the sap thicli and unctuous, of a sour, disagreeable odor, like that 

 of a fermented watermelon, or the tops of potato vines after they have 

 been frosted. In still, moist days, where the blight is extensive in an 

 orchard, this odor fills the air, and is disagi-eeably perceptible some 

 distance from the trees. 



Sometimes the bark bursts, the sap exudes, and runs down, turning 

 black, and its acridity will destroy vegetation upon which it may drop, 

 and shoots at a distance from the trunk upon which the rain washes 

 this ichor, will soon perish. When we come to treat the cause of this 

 disease, it will be important to remember this malignancy of the fluids. 



We are careful to distinguish these appearances, peciftiar to what I 

 suppose ought to be called winter blight, from another and a summer 

 blight. In this last, the leaf is affected first in spots, gradually the whole 

 leaf turns russet-color and drops. Along the .wood may be seen the 

 hardened trail as of a slimy insect, of an ash color. The wood suffers 

 very little by this summer blight, and sometimes none. The winter blight 

 is found on almost all kinds of trees. This summer it has affected the 

 apple, the pear, the peach, the quince, the English Hawthorn, privet, 

 black birch, Spanish chestnut, elder and calycanthus. I enumerate the 

 most of these kinds on authority of J. H. James, of Urbana, Ohio, and 

 C. W. Elliott, of Cincinnati, having observed it myself only on fruit trees. 



II. Theories.— A variety of theories exist as to the causes of this dis- 

 ease. Some are mere imaginations; some are only ingenious, and some 

 are so near to what I suppose to be the truth, that it is hardly possible 

 to imagine how the discovery was not made. 



The injury is done in the fall, but it is not seen until spring or sum- 

 mer, or even the next fall. Thus, six months or a year intervenes between 

 the cause and the effect, and a sufiicient reason for the difficulty of de» 

 tecting the origin of the evil. 



1. Some have alleged that the rays of the sun, passing through vapors 

 which arise about the trees, concentrate upon the branches, and destroy 

 them by the literal energy of fire. Were this true, the yoimg and tende" 

 shoots would suffer most; all pear trees would suffer alike; all moist and 

 hot summers would be affected with blight; herbaceous plants would 

 suffer more than ligneous, all of which results are conti-ary to facts. 



2. Some have supposed the soil to have contained deleterious sub- 

 stances, or to be wanting in properties necessary to health. But in either 

 case such a cause for the blight appears untrue, when we consider that 

 ti'ees suffer in aU soils, rich or poor; that, in the same soil one tree is 

 blighted and the next tree escapes; that they will flourish for twenty 

 years and then blight; that a tree partially diseased recovers, and thrives 

 for ten or more years without recurrence of the blight. 



3. It has been attributed to violent and sudden changes of tempera- 

 ture in the air, and moisture in the earth; from sudden change from 



