16 FRUIT BOOK. 



Are these diseased spots, where the malady first 

 arises, and from whence it is disseminated, the 

 immediate effect of the freezing or the thawing ? 

 We think we are prepared to answer this ques- 

 tion. The fact that these spots, when they occur 

 on the trunk or larger branches, almost invariably 

 appear on the southern side, proves clearly, that 

 it is the too rapid thawing caused by the sun's 

 rays. Now the pear tree appears, so far as re- 

 gards its bark, to be the most tender of our fruit 

 trees. Our climate in winter is often one of the 

 most sudden and extreme variableness. To-night 

 we have the thermometer at zero of Fahrenheit ; 

 the next morning we have a bright unclouded 

 sun, that shines on any dark object exposed to it, 

 with all the warmth of April. The consequence 

 to a susceptible tree is obvious. Any part which 

 happens to be especially exposed, from its posi- 

 tion upon the southern side of the trunk, is of 

 course most likely to suffer from the sudden and 

 powerful effects of the sun, immediately after 

 severe frost. Here, accordingly, we soon find 

 the sap vessels burst, the bark shrivelled, and the 

 poisoned matter accumulated, which is the source 

 of the blight of the ensuing spring and summer. 

 What is the remedy for the frozen-sap blight? 

 We propose to prevent the frozen-sap blight, en- 

 tirety, by white-washing the stems and principal 

 branches of all valuable pear trees, every autumn, 

 after the leaves have fallen. By this simple op- 

 eration, we think the injurious action of the sun 

 will be entirely prevented ; its rays will be, for 

 the most part, reflected, and the rapid thawing of 

 any large part of the bark rendered entirely im- 

 possible. We have ourselves no great admira- 



