49G BACTERIAL DISEASES OF PLANTS 



a humid atmosphere." They say, "It is only during periods of 

 the most brilHant illumination and directly under the glass of 

 the houses, that the intumescences form in quantity. They do 

 not occur in the same greenhouse on leaves which are in a diffuse 

 light, or in the shade." 



In commenting on this statement Dr. Hermann von Schrenk 

 says, "Observations made in the greenhouse of the Missouri 

 Botanical Garden during the present season [1904] on grape 

 vines which were covered with these intumescences, fully 

 bear out the observations made by Viala and Pacottet. The 

 intumescences were formed only on the leaves immediately 

 under the glass, while all the leaves in the shade were free from 

 them." 



Judging from my own observations and experiments, made 

 on the potato, neither "insufficient light" nor "brilliant illu- 

 mination" has anything to do with the formation of intu- 

 mescences, at least with those which are hyperplasias. Also 

 they may appear in the absence of any excess of moisture and 

 when the ventilation is good. 



Not satisfied with the explanation of intumescences above 

 given I made experiments of my own. After some thinking 

 as to how best to begin, it appeared to me that I might imitate 

 defective greenhouse conditions on a small scale by enclosing 

 vegetation in sealed glass tubes. For this purpose I took 

 unshriveled, carefully washed, sound potato tubers of several 

 varieties, soaked them for 30 minutes in 1:1000 mercuric 

 chlorid water to discourage surface organisms, pared away the 

 poisoned surface with sterile knives and cut the remainder into 

 rectangular blocks. These blocks were then dropped with 

 sterile forceps into sterile cotton-plugged test tubes about an 

 inch in diameter and containing at the bottom a wad of cotton, 

 wet with 1 to 3 cc. of distilled water. The cotton plugs were 

 then shoved down a half inch and the top filled with melted 

 sealing wax. In these tubes I obtained the results detailed 

 below. 



In 1910, the Russian botanist, P. Wisniewski, called attention 

 to the production of intumescences on stems by obstruction of 

 the lenticels with vaselin. Five years later (1915) the German, 



