597 



prosenchymatous elements, i. e., they exhibit the characteristic structure 

 of the excrescent wound wood. If the overgrowth edges have united into 

 a connected annual ring, this grows further in such a way that it is sub- 

 divided by medullary rays. The direction of these medullary rays continues 

 that of the medullary rays of the wood formed the previous year. There- 

 fore, this wood has undergone only a temporary interruption in the brown 

 dead tissue. 



The changes and tissue excrescences described are never found in 

 wood of the current year. 



(iothe thinks the bead-like appearance of the tissue excrescence, whicli. 

 growing extensively radially, splits the old bark, is explained by a complete 

 "overlapping, inward growth" of the overgrowth rolls, which are present 

 most abundantly at places on the vine lying about 30 cm. above the surface 

 of the soil. Examination shows that,, starting at such places, the number 

 and extent of these swellings decrease away from as well as towards the 

 soil; close to it. and about one meter away from it, they occur very rarely. 

 With a slight development of the disease, the attacked trunks may vegetate 

 for several years and then still produce bearing wood. With a greater 

 development of the canker swelling, the wood, lying above it, dies. 



The rapidity, with which the canker swelling is produced, is proved by 

 the fact that, on August 8th, i)lants were found in which the grafting tajie 

 lay embedded 0.75 cm. in the tissue excrescences. Therefore, the entire 

 canker swelling, 2.5 cm. thick, can only have been produced after the time 

 of grafting (in May), for it can not be assumed that a scion would have 

 been inserted in a diseased vine. 



Gothe has proved by the following experiment that the injuries to the 

 cambial ring take place in the spring. In April, when the vines were 

 pruned. 12 strong bearing vines were tapped, between two nodes, with a 

 dull iron, in such a way that an injury to the cambial layer could be as- 

 sumed. Cilass tubes were then shoved over the injured places and the 

 openings closed. The first traces of the swellings could be proved as earlv 

 as June 8th, while on specifically scabb}- vines the tissue excrescences did 

 not appear until June 20th. Up to autumn, perfectly normal scab struc- 

 tures continued to form in the glass tubes, with also the same anatomical 

 structure as naturally formed excrescence edges. 



Spring frost may be considered as the cause of these excrescences in 

 nature. Most of the literature which proves the appearance of grape 

 canker after spring frosts also favors this assumption^ It is also strength- 

 ened by the discovery that grape canker occurs only in the so-called frost 

 holes. Gothe cites in this connection, an example from a vineyard which 

 began on a small slope, passed through a hollow and rose again on the 

 opposite slope. On both slopes the plants were healthy, but in the hollow 

 were found to have been attacked by the disease. In a subsequent test, the 



1 Gothe cites v. Babo. Weinljau, p. 305; Dornfeld, Weinliausohule, 

 Kohler, Der VVeinstock und dor Wein, p. 20'.; du Breuil, L.es Vignobles. 



