418 BOARD OF AGKICULTURE. 



is known, but what otbei* decomposition is effected, if any, I know not. 

 The effect of congelation upon the descending sap of pear and apple trees 

 is to turn it to a viscid and 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 mo 

 means of knowing. 



The effect of freezing upon the condition of sap vessels is better 

 known. Congelation is accompanied with expansion, the tender vessels 

 are either burst or lacerated, the excitability of the parts 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 obstructed by a thjckening of their sides. (Lindley's Hox'ticulture, 

 pp. 81, 82.) The fruit trees of 1843 were brought into a morbid state, the 

 sap thickened and diseased, the passages lacerated, obstructed and, in 

 many instances, burst. The sap elaborated, and now passing 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 gradu- 

 ally collect at the junction of fruit spurs, the forks of branches, or 

 wherever the condition of the sap vessels favored 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 develop 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 a practiced eye will 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 alburnum, which has probably been 

 but little injured, the leaf puts out, and no outward sign of disease 

 appears, nor will it appear until the leaf prepares the doTvmward current. 

 May, June and .July are the months when the growth is most rapid, and 

 when the tree requires the most elaborate sap, and in these months the 

 blight is fully developed. When the descending fluid reaches a point 

 where, in the previous fall, a total obsti'uction had taken place, it is as 

 effectually stopped as if the bi'anch were girdled. For the sap which had 

 been lodged there would, by the winds and sun, be entirely dried. This 

 would not be the case if the sap was good and the vitality of the wood 

 unimpaired, but where the sap and vessels are both diseased, the sun 

 affects the branch of the ti'ee just as it would if it were severed and 

 lying on the ground. There will, therefore, be found upon the tree, 

 branches with spots where the bark is dead and shrunk away below the 

 level of the surrounding bark, and at these points the current downward 

 is wholly stopped. Only the outward pai't, however, is dead, while the 

 alburnum or sap wood. Is but partially injured. Through the alburnum 



