Its cause, and a remedy for it. 449 



produced by cold upon the ascending sap, or on the cambi- 

 um, nor upon the elaborated descending current. There is 

 reason to suppose that the two latter only suffer, and prob- 

 ably only the last. That freezing and thawing decompo- 

 ses the coloring matter of plants is known ; but what other 

 decomposition, if any, is eifected, I know not. The effect 

 of congelation upon the descending sap of pear and apple 

 trees, is to turn it to a viscid, unctuous state. It assumes 

 a reddish, brown color ; becomes black by exposure to the 

 air ; is poisonous to vegetables even when applied upon 

 the leaf Whether in some measure this follows all degrees 

 of congelation, or only under certain conditions, I have no 

 means of knowing. 



The effect of freezing and thawing upon the tissues and 

 sap vessels, is better known. Congelation is accompanied 

 with expansion ; the tender vessels are either burst or lace- 

 rated ; the excitability of the parts is impaired or destroyed ; 

 the air is expelled from the eeriferous cavities, and forced 

 into the passages for fluids; and lastly, the tubes for the 

 conveyance of fluids are obstructed by a thickening of their 

 sides. =^ The fruit trees, in the fall of 1S43, were, then, 

 brought into a morbid state, — the sap thickened and dis- 

 eased ; the passages lacerated, obstructed, and probably, in 

 many instances, burst. The sap elaborated, and now pass- 

 ing down in an injured state, would descend slowly, by 

 reason of its inspissation, the torpidity of the parts, and 

 the injured condition of the vessels. The grosser parts, 

 naturally the most sluggish, would tend to lodge and grad- 

 ually collect at the junction of fruit spurs, the forks of 

 branches, or wherever the condition of the sap vessels fa- 

 vored a lodgment. In some cases the passages are wholly 

 obstructed ; in others, only in part. 



At length the spring approaches. In early pruning, the 

 cultivator will find, in those trees which will ere long de- 

 velop blight, that the knife is followed by an unctuous sap, 

 and that the liber is of a greenish yellow color. These 

 will be the first signs, and the practised eye may detect 

 them long before a leaf is put forth. 



When the season is advanced sufficiently to excite the 

 tree to action, the sap will, as usual, ascend by the albur- 



* Lindley's Horticulture, 81, 82. 

 VOL. X. — NO. XII. 57 



