HE plausible and almost uuiversally received 

 opinion that the frozen sap blight in the peai 

 tree is caused by the rupturing of the tissues, owing 

 to the expansion of the sap when converted into ice, is not suffi- 

 ciently confirmed by facts, and the results of rupture from other 

 causes to permit a discontinuance in investigation. 



It is a well-authenticated fact that succulent plants are more 

 susceptible of the influence exerted by heat and cold than those 

 which form short, jointed, fii'm wood. A pear tree planted in damp 

 soil is liable to produce soft, saturated tissue ; and in direct pro- 

 portion that the tissue is rendered moist, is the susceptibility and 

 conducting power of the tree nicreased. A pear tree of a similar 

 variety planted in dry ground, grows slow, and creates hard tis- 

 sues, which diminishes the conducting power, is not so sensitive 

 lo extraneous influences, and therefore is better prepared to com- 

 bat the extremes of heat and cold. Frost exerts itself specifically ; 

 its action can only be experienced w'here humidity exists. When 

 dilatation takes place by the formation of ice in the cellular tis- 

 sue, they are not lacerated, but simply separate, as these vesicles 

 possess, in a limited degree, contractile and expansive powers, 

 particularly succulent plants. This power diminishes as the wood 



