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stem node into the roots, produced at that point, and may be found in the 

 whole part of the axis which is still green, up to the ribs of the last leaves. 



Especially striking is the sap turgescence in the apparently perfectly 

 healthy parent tuber which exhibits some cells with large unconsumed starch 

 grains. The groups of cells containing the starch lie scattered in the very 

 turgescent parenchyma of the tubers, which shows scarcely any traces of 

 solid cell contents, while the nuclei are large. 



It is further noteworthy that, just as healthy and diseased shoots may 

 be produced from one tuber, the characteristics of disease on the same stem 

 can often be restricted to definite areas. Healthy eyes may develop on 

 diseased stems and diseased stems are found in which only half of the vas- 

 cular bundle ring is blackened. 



Thus, like other diseases connected with the discoloration of the ducts, 

 leaf curl begins to manifest the first symptoms of disease at the peripher}-. 

 The cuticle blackens most of all. The cell contents began to change color 

 at first to a weak inky color, until the walls and contents have become uni- 

 formly brown, after which the epidermal cell collapses. 



Wliere the epidermis borders on the collenchymatous tissue, the dis- 

 coloration advances in its walls. They become slightly yellowish at first, 

 then reddish yellow (in some varieties a peculiar blood red), and finally 

 brown. This discoloration of the walls, which seems to spread rapidly 

 tangentially, recalls enzymatic activities. 



The further course of the disease differs in the different varieties, 

 probably because the cell walls vary in construction, some being more loose- 

 ly built, others more solidly. In Early Puritan it was observed that the 

 browned cell walls could be attacked by a granular decay, in which small 

 rod-like bacteria probably participated. In these cases the tissue disap- 

 peared, while holes and depressions appeared in the bark tissue of the 

 stem and mycelium was found. In Early Puritan the depressions deepened 

 to the wood ring and, as the disease advanced, their pressure could be dem- 

 onstrated even on the still green tips of the stems. The browning of the 

 ducts, however, did not proceed from them; it began at the base of the 

 stem and spread only in the vascular system. At the torn places processes 

 of healing often manifested themselves in the pouch-like elongation of the 

 adjacent, healthy bark parenchyma cells. 



The statement given above, that the symptoms of disease do not uni- 

 versally appear uniformly relates, for example, to the appearance of brown 

 specks on the uncurled leaves. However, in the petioles of these leaves 

 there is exactly the same pale inky filling of the ducts which, in some cases, 

 thickens to a grainy slime ; the walls of the ducts also are browned. 



The characteristics here described occur separately also in other plants 

 with an excess of nitrogen. If these symptoms are compared with the re- 

 sults of earlier observations, leaf curl may be described as follows. The 

 diseased condition appears most luxuriantly and abundantly on tender early 

 varieties. The harvested tubers are immature, being distinguished by a 



