108 GENERAL REMARKS 



truth many trees, are destroyed by the operations of a girdler. This is a cause which is 

 easily ascertained, the whole effects of which resemble precisely the operations we often 

 perform upon trees for the purpose of destroying them; and we may add, that the pheno- 

 mena attending the death of the tree or limb is precisely the same. The source of nutri- 

 ment in both cases is cut off, and the limb or tree dies simply of starvation. There is in 

 neither case an infused poison, but, merely a destruction in the continuity of the parts which 

 transmit the sap from the roots to the branches. In this case we are able to trace the death 

 lo a satisfactory cause, and our verdict on a post mortem examination must be, death from 

 girdling. 



The late Prof. Peck, as is well known, discovered the cause of one species of blight, in 

 the insect called the Scolytus pyri, which eats around the branch beneath the bark. 



This kind of blight must necessarily be distinguished from the blight which we have 

 described, and which we consider a true vegetable gangrene. The remedy may be the 

 same, viz., extirpation. In the one case extirpation is performed for the purpose of de- 

 stroying the destroyer ; in the other, it would seem for the purpose of preventing the ming- 

 ling of tainted fluids with those which are healthy, and by which it is to be feared the dis- 

 ease may be extended to the whole system. In support of this view of the matter, it may 

 be observed that it is an established fact that the contact of diseased parts with sound ones, 

 or the mingling of diseased fluids with the healthy, is invariably injurious; and that under 

 such circumstances the disease propagates itself in a manner which may be likened to the 

 effects of leaven. This, it is true, is one of the oldest ideas of cause in accounting for 

 diseased or unhealthy action, though of late it has been brought before the public in a dress 

 somewhat new. As we are now speaking of the cause of blight, it is but right that we 

 should refer to a cause which has been assigned by a distinguished writer upon horticulture. 

 The writer referred to maintains that it is caused by sap which has frozen during the pre- 

 ceding winter. 



There are many objections to this as a cause of the blight here described. 



1. If the sap is frozen, and is thereby changed in its properties, it can hardly be main- 

 tained that it is capable of performing the part of a nutritious fluid, and possess the required 

 properties which shall fit it for the development of leaves. It is but rational to infer that 

 sap, when changed essentially by any cause, should act in the first period of its circulation 

 in its usual way, and then subsequently, after having performed the exact purpose of 

 healthy' sap, at last can cause the death of a part which it had brought into life and exist- 

 ence. Besides, it is no where shown that frozen limbs always result in their destruction, or 

 or in the destruction of the sap. Repeated freezing and thawing will undoubtedly destroy 

 the vegetable organs, but in these instances the effect is immediate, and the limb or tree 

 never puts forth its leaves at all. In the county of St. Lawrence, and in other parts of the 

 Slate, where frost destroys a tree or a part of it, there is an entire end of it. It never ex- 

 hibits a vigorous life, it never puts forth strong and healthy leaves and blossoms, but it is 

 actually a dead tree, or a dead part, when the cause has thus acted upon it. 



