439 



The intumescences on grape leaves have on the under side the form of 

 ;land-Uke elevations which often coalesce and are indicated on the upper 

 leaf surface by yellowish and at times somewhat raised places. They are 

 produced by tube-like outgrowths of the spongy parenchyma lying under 

 the epidermis ; the cells of this spongy parenchyma are poor in solid con- 

 tents and closely pressed against one another by the distension. With their 

 increasing over-elongation, the epidermis is browned and ruptured. 



In the beginning only the cells lying directly beneath the epidermis are 

 affected, but usually, after the distension begins, the cell layer next below 

 is attacked and it is usually this which later is most elongated and its cells 

 not infrequently divided by cross walls. The cells forming the centre of the 

 swelling are the longest and most slender and stand exactly perpendicular to 

 the outer surface of the leaf, while those laterally adjacent are arranged 



'■A 



Fig. 77. Part of a knot-like intume.scence on the stem of a grape. (Orig.) 



slantingly like a fan, decreasing in length, increasing in width. The presence 

 of starch could not be proved. In the most extreme cases observed, all the 

 cells of the mesophyll, up to the palisade parenchyma of the upper side, take 

 part in this elongation. I did not observe, however, that the palisade 

 parenchyma had been attacked. 



These intumescences are not infrequent in vineyards and cases may be 

 found showing their cause most clearly. In the course of years material 

 has come most abundantly to my hands. I quote from the report of the 

 court gardener, Mr. Rose. 



He had a grape house planted with 14 vines ; of these, six were Black 

 Hamburgs (Blauer Frankenthaler), one of these was planted where the hot 

 water pipe entered. Therefore, the temperature was higher and the humid- 

 ity very great. 



This vine alone developed intumescences to such a degree that the 

 under side of the leaves seemed almost felty. A Royal Muscardine vine 



