76 C|e §Ktkmx& <p;flnt|lg. 



blighted similarly ; all the shoots of the past sea- 

 son, however, being green. 



This invasion had, evidently, taken place in Sep- 

 tember, judging from the dryness of the deadened 

 bark and tissues. In all cases the disease was in the 

 body, extending only 2 or 3 inches up the limbs, 

 and generally reaching down on the stem below the 

 branches to a distinct line running obliquely around 

 the tree, below which all was green. In 2 or 3 in- 

 stances, only the body was killed to the ground. 

 Thirteen deaths, in all, had occurred in the season, 

 being one in every 38 trees, and averaging about 2 per 

 cent, yearly for the two years. My city neighbors in 

 the valley lost from 20 to 25 per cent, of their trees 

 I in each of the years. Another neighbor, residing 

 a one-fourth of a mile west of me, upon still higher 

 ; ground, had no appearance of the disease in his 

 ! trees during either year. His immunity is attribu- 

 I table, I think, to his elevated site, an entire absence 

 j of local miasm, and being beyond the reach of - the 

 i fogs and vapors of the valley. 



In each year of the disease in my orchard, some 

 of the trees attacked were thrifty, some of medium 

 vigor, and some feeble ; the variety or character of 

 the tree (whether on Pear or Quince) making not 

 the slightest difference, — except that the Seckel 

 escaped better than most varieties, though not en- 

 tirely. 



The inquiry next arises. What theory do these 

 facts sustain ? Certainly not the "frozen sap" one. 

 They show that the disease may originate at any 

 \ period of the growing season, and not in the Fall 

 1 only. If the cause were attributable to the freezing 

 I of the sap, would not the entire sap of the tree or 

 I branch become corrupted, carrying death to all the 

 parts, without stoppinsr at a distinct line or point on 

 the body? Why should freezing render the sap of 

 the Pear poisonous ? True, the Pear is a cultivated 

 tree and not a natural one. But the same is true 

 of the Cherry, Peach and Plum, and why does not 

 I their snp, also, become poisonous by freezing? The 

 j poisoning of the sap, may, I think, be referred more 

 rationally to other causes. 



How much consideration the other theories — 

 those attributing the cause of blight to "changes of 

 temperature" and "fungus" — are entitled to, re- 

 mains yet to be seen. While there is much reason 

 to doubt that either is the cause of the disease, there 

 exist reasons for believing that each is a partial 

 cause, and that the two combined may prove the 

 real cause. It is well known, in medicine, that the 

 - human system is affected by sudden changes in the 

 ^ temperature of the atmosphere, or in raiment or 

 food. These changes may not produce disease at 



the time, but they often throw the system into an 

 abnormal state, deranging it, and predisposing it to 

 disease. As an instance, the case of a man may be 

 cited who, on the first occasion, partakes largely of 

 some article of green or unripe food, whereby func- 

 tional der ngement, or, possibly, diarrhoea, en- 

 sues. If, during this derangement, he is brought 

 into contact with a cholera atmosphere, the result 

 is an attack of the cholera ; while the man who has 

 not partaken, will probably escape, though equally 

 exposed. 



A sudden change of the food of stock, and animals 

 generally, from dry to green food, often produces 

 what is cailed "scours." These derangements in 

 the animal svstem, most of which are so slight as 

 not to be observable, throw it out of its normal con- 

 dition, and predispose it to an attack of disease from 

 outward causes. A cholera atmosphere (an out- 

 ward cause) does not of itself produce cholera in the 

 human system ; nor does an atmosphere charged 

 with ague miasm produce, of itself, fever and ague. 

 This may be proven by immersing anv number of 

 persons, whose systems are healthy and normal, in 

 such atmospheres. They will escape the disease — ■ 

 their systems being able to throw off the malaria. 

 But, if persons whose systems are deranged Oi ab- 

 normal, be thus immersed, they will probably be 

 attacked. 



This indicates that many diseases of the animal 

 kingdom, such as endemics and epidemics, have at 

 least two causes. — one of which is infernal, and 

 another external ; or, to use medical phrases, pre- 

 disposing cause, and an exciting cause. Neither of 

 these is, properly, the cause in itself; but when 

 both the causes unite or occur at the same time, 

 they, as combined, constitute more strictly, the 

 cause. 



In the next p. ace it may be asked. Why may not 

 trees and othe ■ vegetable products be subject to sim- 

 ilar rules concerning diseases which affect them? 

 They inhale and take up food and drink for their 

 support, — they live and they groiA), — as well as ani- 

 mals. Reasoning analogically, therefore, it would 

 seem that many diseases of trees are brought on by 

 a plurality of causes, and especially so of those 

 classes of trees which are produced by cultivation or 

 artificial means. 



Trees growing in a state of nature develop more 

 slowly and healthily, and are rarely subject to dis- 

 ease. Cultivated Pears and Grapes are, perhaps 

 above all other fruits, artificial productions, and are 

 more subject to disease than other fruits. They are 

 the best of fruits, and their successful cultivation 

 requires much labor, united with much thought and 



