156 EXPERIMENT STATION. [Jan. 



tobacco and other allied plants. It occurs ou tobacco, also, 

 without pruning in the Held, due to some functional disarrange- 

 ment in all probability; but in the case of tomato we have not 

 been able to find a case in which the disease occurred on a plant 

 which was allowed to grow normally, that is, without pruning. 

 Plants in the field are also not so susceptible to it. and it is 

 rather difficult to conceive just why it is that under similar 

 conditions, but with different plants, we sometimes get the char- 

 acteristic mosaic disease and sometimes only a condition such as 

 the one under discussion. 



Relation of Root Area to Intensity of Disease. 



In the course of our ex])erinients it was observed that in the 

 same locality, with the same kinds of trees, there was a marked 

 difference in the intensity or severity of the malformation. It 

 was thought that the size of the original tree and its correspond- 

 ing root area might bear some relation to the severity of the 

 disease. Rough estimates were made of several root systems 

 from which first-year sprouts were growing which were dis- 

 eased, and in general it was found that the larger the root area 

 the more distortion of the leaves. This seemed to l)e the gen- 

 eral rule, but from the limited number of observations we were 

 able to make it would be unwise to make a positive statement 

 as to the absolute truth of this observation. 



When young trees had been cut downi or killed by burning, 

 there was not such severe distortion, but more of a tendency to 

 produce abnormally large leaves. As a result of our observa- 

 tions it may be stated that there is a relationship existing be- 

 tween the amount of active root surface and the severity of the 

 trouble along the lines we have pointed out. 



It has been stated elsewhere in this article that the severity 

 of the disease diminishes from year to year as the plant grows 

 older, and it would be natural to ex])ect such a recovery for two 

 reasons : first, the shoot is larger the second year than the first, 

 thus having more leaf surface to effect transpiration, respira- 

 tion, carbon assimilation, etc. ; and secondly, some part of the 

 root system, owing to lack of food (available), which the first 

 year's leaves have been unable to su])ply, has died from general 



