ABOUT FRUITS, FLOWERS AXD FARMIXG. 403 



or wherever the condition of the sap-vessels favored a lodg- 

 ment. In some cases the passages are wholly obstructed ; 

 in others, only in pait. 



At length the spring approaches. In early pruning, the 

 cultivator will find, in those trees Avhich will ere long deve- 

 lop 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 sufliciently to excite the 

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

 num, which has probably been but little injured ; the leaf 

 puts out, and no outward sign of disease appeai-s ; nor will 

 it appear until the leaf prepares the downward 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 the point where, in the 

 previous fall, a total obstruction had taken place, it is as 

 effectually stopped as if the branch were girdled. For the 

 sap which had lodged there would, by the winds and sun, 

 be entirely dried. This would not be the case if the sap 

 Avas good and the vitality of the wood unimpaired; but 

 where the sap and vessels are both diseased, the sun affects 

 the branch on the tree just as it would if severed and lying 

 on the ground. There will, therefore, be found on 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 outicard part, however, is dead, while the albnr- 

 num^ or sap-wood, is but partially injured. Through the 

 alburnum, then, the sap from the roots passes up, enters 

 the leaf, and men are astonished to see a branch, seemingly 

 dead in the middle, growing thriftily at its extremity. No 

 insect-theory can account for this case ; yet it is perfectly 

 plain and simple when we consider that there are two cur- 



