306 Agricultukal Expekiment Station, Ithaca, N. Y. 



radial elongation of the phellogen causes the periderm to be raised in 

 the form of a blister. Beside the radial elongation of the phellogen 

 cells they are also very much distended. This distension continues 

 until the cell walls are no longer able to stretch because they become 

 BO thin that they break and the cells collapse. This collapse of the 

 phellogen cells causes the collapse of the blisters and in drying these 

 affected areas are depressed below the normal surface of the twig. 

 Also the dying tissue forms a nidus for such saprophytic fungi as the 

 Fusarium which was in many cases present. The dropseal swelling of 

 the tissues is of the same nature as that which occurs sometimes with 

 tomatoes when grown under conditions which favor rapid and con- 

 tinuous root absorption and at the same time hinder transpiration, or 

 growth. A thorough study of this trouble with the tomato was 

 made last winter by the author and published in bulletin No. 55, May, 

 1893, of the Cornell Station. To this the reader is referred for a full 

 discussion of the unequal operation of the physiological laws which 

 induce the trouble, and for the bibliography. 



In the case of the tomato (edema the unequal operation of the 

 physiological laws was due to certain unfavorable conditions of 

 greenhouse lighting and heating. This would not apply to the 

 case of the apple trees which were grown out doors. But since 

 the trouble was like in kind, the cause would probably be found 

 in some condition of soil, cultivation, or pruning of the trees, 

 which would favor root absorption and hinder transpiration, or 

 growth, at a sufficient number of points on the tree to take charge 

 of all the water which the roots absorbed. Inquiry of the owner 

 developed the fact that the soil in the young orchard was very 

 fertile and well worked, and that the conditions, so far as soil was 

 concerned, were very favorable for rapid root absorption and 

 growth. In fact the trees grew very luxuriantly and were the 

 marvel of the neighborhood. But during the winter and eai'ly 

 spring they were very severely pruned. According to the owner 

 they were pruned very close, leaving only the main limbs and twigs 

 and a few secondaries, and the new growth was cut back one-third. 

 This left but few growing points. When root absorption and growth 

 began in the spring, there being no leaves to discharge the excess of 

 water through transpiration, the few growing points could not dispose 

 of the excess. Consequently the thin- walled phellogen tissue could not 

 stand the strain. Figure 2 represents a portion of a cross section of 

 one of the blisters; a, periderm; b, phellogen; e, inner layer of cells 

 developed from phellogen; d, bast fibers; e, cambium; /, medullary 



