150 TKANSACTIONS OF THE ILLINOIS 



But T had not investigated the subject and could not substitute any 

 theoiT for the one advanced. Subsec|uent talk and correspondence 

 with the honorable Secretary led to my taking this subject as one to 

 be investigated during the past season, the following report upon 

 which I beg leave to submit for your consideration: 



I find several things operating to bring about the destruction of 

 trees, among which may be mentioned insects, sun-blight, fungi, and 

 last, but not least, the so-called severe winters of the northwest. All 

 but the last of these, so far as apple trees are concerned, are in oper- 

 ation more or less all over the State. It may be as well, perhaps, to 

 consider the work of insects in connection with the other parts of 

 the topic; and first we will take 



SUN-BLIGHT. 



The question may be raised, " What is sun-blight? " Every one 

 who has been about orchards much has noticed that some trees show 

 a peculiar roughness and blackening of the bark on the southwest 

 side of the trunk and large limbs. Later the bark dies, and in the 

 course of a year or two begins to break off, the extent of these 

 patches extending so that the whole of that side of the tree is in- 

 volved, and it may extend more or less around the south and west 

 sides. The term sun-blight, by which this disease is known, seems 

 very appropriate. 



The manner in which this is produced seems to be about as fol- 

 lows: During very cold winter days the trees, as well as other objects 

 around, are frozen. If the day be moderate, still and clear, the sun 

 shines with considerable Avarmth on the south side of objects, reach- 

 ing its culmination of heat at about 2 o'clock in the afternoon. At 

 such times whatever heat there is comes from the north, and hence 

 the south side of the tree is sheltered from the breeze while under 

 the influence of the sun's rays. The result will be that the tree will 

 become thawed on that part Avhere the sun shines the hottest, or on 

 the southwest side. This gradual thawing will cause a slight flow 

 of sap in the outer sap-wood and inner bark, drawing more moisture 

 to these parts than was there before. This will be the case to a 

 greater degree where the ground is not frozen to a great depth, for 

 then there will be a slight activity in the roots in the unfrozen 

 ground that may connect with the thawed portion above if there be 

 only a few inches of frozen soil. At night the tree will freeze again, 

 to be thawed out on the following day if it be pleasant. In South- 

 ern Illinois, as is well known, we have every winter several, days in 

 succession of just such cold, pleasant weather. 



The hard, wood cells may be but little injured by this thawing 

 and freezing, under an increase of moisture, but the tender cells of 

 the extreme outer part of the wood (the cambium layer), and the 

 tender cells of the inner bark will have their contents so changed 

 that death to that part will be the result. To make this clear, let 



