their vessels? We have been able to- find so little written 

 upon vegetable morbid anatomy (probably from the want 

 of access to books), that Ave can give but an imperfect account 

 of the derangement ^^roduced upon the circulating fluids 

 by congelation. We cannot state the specific changes pro- 

 duced by cold upon the ascending sap, or on- the cambium, 

 nor upon the elaborated descending current. There is rea- 

 son to suppose that the two latter only sufier, and probably 

 only the last. That freezing and thawing decompose the 

 coloring matter of plants is known ; but what other decom- 

 position, if any, is effected, we know not. The effect of con- 

 gelation 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 con- 

 gelation, or only under certain conditions, we have no means 

 of knowing. 



The effect of freezing and thawing upon the tissues and 

 sap-vessels is better kno-wm. 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 aeriferous cavities, and forced 

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

 conveyance of fluids are obstructing by a thickening of their 

 sides.* The fruit-trees, in the fall of 1843, 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, natu- 

 rally the most sluggishy»would tend to lodge and gradually 

 collect at the junction of fruit-si)urs, the forks of branches, 



* Lindley's Horticulture, p. 81-82. 



