ON PEARS. 



Ill 



1. 



portion of it. The limb is constricted, and is nearly one quarter smaller than the adjacent 

 parts above or below. This constricted portion appears so perfectly dead and dry, that it 

 seems impossible for the sap to pass through it and reach the vigorous and living portion 

 bej'ond ; which is not only bearing large leaves but also fruit, which is also equally as 

 large and promising as that upon any of the unaffected limbs. 



The effect of the disease as exhibited in very numerous instances, is much the same as 

 that which follows from ringing a branch ; a process by which the circulation, as is main- 

 tained, is interrupted. Its descent to the root is at least partially prevented, by which 

 there is an accumulation at all times of nutritious fluids in the limb above the removed or 

 injured bark and wood. The constriction where the disease is seated is mechanically 

 arrested, however, with the ascent and descent of the sap; for here it is evident, by the 

 dry state of this portion of the limb, that its vessels are nearly impervious ; and after a 

 short time they become entirely so — the dis- 

 ease passing from outside to inside, and not in 

 the opposite direction. The circulation, there- 

 fore, is sustained by the interior. It would 

 seem from an inspection of the dying branches 

 that it is almost impossible, in many instances, 

 for the sap to pass along the limb ; still, there 

 is no doubt that this it does so long as a green 

 leaf appears. 



The following cuts exhibit the facts we have 

 stated; and it may, if followed out, throw new 

 light upon the circulation of sap, and of the 

 nutrition of vegetables. 



Fig. 1. Part of a blighted branch of an 

 apple tree, which was taken from the garden 

 of E. P. Prentice, Esq., of Albany. 



a, Dead bark and wood ; b, living bark and 

 newly formed wood ; c, constricted portion of 

 the stem, and dead upon the outside; e, inte- 

 rior of the stem, showing signs of life ; f, liv- 

 ing and luxuriant growth of part of the branch. 



In this example there is quite a thickened 

 state of the branch at a, which in the speci- 

 men, is strongly contrasted with the part be- 

 yond the dead portion ; as it is about J thicker 

 by the formation of new wood since it was 

 attacked by the blight. Most of the new 

 growth has taken place since the time when 

 a branch usually acquires the length of stem 

 for the season. In the bark, or immediately 



