328 The Frozen Sap Blight. 



increases in dryness. If the frozen sap blight were attributable 

 to the bursting of the cellular tissue, and the consequent displace- 

 ment of the fluids, and the interruption to the economy of the 

 plant, then similar disastrous consequences would be realized, in 

 partially severing a tree with a knife, or where bruises or disbark- 

 ing accidentally occurs : in the latter case there is no apparent 

 diminution of vigor in the tree ; on the contrary, but a short pe- 

 riod elapses before the destroyed tissue is replaced, and performing 

 its functions in a healthful manner. It is not freezing, then, nor 

 the laceration of the tissue that causes death in a pear tree, but 

 sudden thawing. When a sudden thaw transpires, the compo- 

 nents of the sap do not recombine ; the heavier portion precipi- 

 tates in coagulated atoms, and in this form is incapable of elabo- 

 ration. Nothing remains but a watery fluid, which is entirely de- 

 void of the vital principle of sap. Chemical decomposition takes 

 place, and the fluids become viscid. Under these circumstances, 

 a tree on the approach of warm weather will expend the perfect 

 sap remaining in the branches in putting forth leaves, which, 

 meeting with no nourishment, in a short time die. Occasionallj' 

 but one side of a tree is affected by the thaw, and we have invari- 

 ably noticed where this occurs, that it is the side directly exposed to 

 the rays of the sun. In such instances the tree rarely dies. The side 

 containing the pure sap in its upward progress takes up the in- 

 spissated fluid, and conducts it to the leaves, where it is rejected 

 in the , shape of reddish brown tubercles, which will continue mak- 

 ing their appearance until the tree is entirely divested of impuri- 

 ties. Prof Turner, who had observed this peculiarity, concluded 

 that it was an entirely different kind of blight, instead of which it 

 is a modified form of the frozen sap blight. 



A frozen potato, if thawed slowly by plunging it in cool water, 

 will receive but little injury, but if thawed quickly it undergoes a 

 wonderful change. The starch which it previously contained, al- 

 most entirely disappears, and in its place you have sugar. When 

 a frozen plant is subjected to the influence of light and heat, by 

 slowly increased gradations of intensity, the several constituents 

 of the vital principle rc-assume their relative healthful positions 

 regarding each other, and the economy is but slighily disar- 

 ranged ; quite the reverse occurs when heat is applied sud 

 denly 



