402 PLAIN AND PLEASANT TALK 



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

 upon vegetable morbid anatomy (probably from the want 

 of access to books), that we fan give but an imperfect account 

 ot' the derangement produced 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 suffer, and probably 

 only the last. That freezing and thawing decompose the 

 coloring matter of plants is known ; but what other lrc. mi- 

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

 gelation upon the descending sap of pear and apple-trc< <, 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 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 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 full of 1843, were thru 

 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 sluggish, would tend to lodge and gradually 

 collect at the junction of fruit-spurs, the forks of branches, 



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



