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DISEASES. 



Plants, like animals, are liable to disease just in 

 proportion as they are made to live in a climate dif- 

 fering little or much from that of the country in which 

 they are natives. The climate of Persia differs greatly 

 from that of Great Britain, and, as a consequence, the 

 peach is here subject to peculiar diseases unknown as 

 its ravagers in his native habitat. The chief differences 

 between the climates of the two countries are the 

 greater wetness of that of Great Britain, and the 

 greater vicissitudes of temperature during its sum- 

 mers. To these differences may be traced the origin 

 of all the diseases to which this fruit-tree is liable. 



Gumming is an issue or extravasation of the sap of 

 the peach tree, arising usually from its being formed 

 more rapidly than it can be conveyed away by the 

 sap vessels. When this occurs rupture must take 

 place, for the force with which it is propelled during 

 circulation, and consequently the force acting to burst 

 the vessels during any check, is very much greater 

 than could have been expected, before Mr. Hales de- 

 monstrated it by experiment. Now, we know that a 

 much less pressure than any of those he ascertained 

 would be capable of bursting the delicate membranes 

 of any of their exterior descending sap vessels, and it 

 is in such outer ducts that the injury first occurs. 

 When one exterior vessel is ruptured, that next be- 



