98 TRANSACTIONS OF THE ILLINOIS 



made of certain vegetable diseases, and of some of the habits of several of our insect 

 foes, not before understood, will mainly constitute the base of my present remarks. 



PEAR, APPLE AND QUINCE TREE BLIGHT. 



Before we can hope to vitalize by artificial means structures so delicate as are those 

 which we have determined are the cause of bhght, it will be necessary to possess a 

 thorough knowledge of the laws of vegetable growth. 



So small are the structures which I propose to figure and describe, especially in the 

 germ state, that millions of them might be dispersed among the wood cells contained 

 within a cubic inch, with a scarcely perceptible increase of its bulk. The process of 

 vegetating them is such as to require the greatest nicety in manipulation. 



^Vhoever can, from day to day, so control the conditions aflecting plant growth as to 

 cause leaves of fruit trees to root and branch, may hope artificially to vitalize the 

 spores of blight. The nicety of manipulation, however, will not end with vitalization. 



To figure and describe these mucilaginous globules, for such plants causing blight in 

 trees appear to be, taxes to the utmost our sight, our skill and endurance. The 

 slightest breath vriU detach those plants that are fuUy grovm from the parent or point 

 of attachment and disperse them ; and when by chance we have them under observa- 

 tion, the powerfully reflected light to which we have to subject them, quickly burns 

 or dries them iip. These and many other diflaculties, a full enumeration of which I 

 shall not now attempt, constantly interpose, requiring on the part of the operator 

 leisure to observe, skiU in handling, and a determination to overcome obstacles in the 

 way of success. 



If we examine closely the bark of pear trees sometime in the month of May, or at 

 any time until near the time the tree completes its growth for the season, we may find 

 in the outside layers of the Uving bark, on those trees subject to blight, little raised 

 patches presenting to the eye something oi a spongy appearance. This raised spongy 

 bark is not confined to any particular varieties, nor will particular branches, or any 

 certain parts of trunks of trees, be found more likely to be free than other parts; slow 

 growing sorts, or those that mature their growth early in the season, are most exempt 

 from the killing eflects of blight, as will appear in the course of my remarks . If we 

 cut the spongy bark, of which I have spoken, into very small pieces, and for conven- 

 ience in handling put a pin through each piece, then place a number of these small 

 pieces of bark in a bottle containing enough moisture to aflbrd the humidity needed 

 to excite vegetable growth ; then cork and put the bottles containing these specimens 

 in a box and cover the whole with damp saw dust or other material to exclude light. 

 Next, the box with its contents, for a period of from two, four or six days, must be 

 kept at a temperature from 80° to 100° . At the end of this time, if we take from the 

 bottle some of these small pieces of bark and place them under a microscope, manify- 

 ing fi\e or six hundred diameters, there will be seen on the outer edges of some of 

 them Httle cellular like forms, attached to the sides, or partly, protruding from little 

 crevices or abrasions in the bark. If we observe closely, it will become apparent that 

 these little forms which come under observation, and which at first sight appear to be 

 identical, are quite different, and may properly be divided into two classes. 



The one I shall first briefly describe and figure, which I do for comparison, is a 

 wood cell, and was made out of the materials which the tree is constantly elaborating 



