42 EXPEULMEXT STATION. [Jan. 



only of the '" mosaic " of tobacco and tomato. Experimental 

 data have Ix-cn obtained to a certain extent on these allied dis- 

 eases and will be presented in a futnre report. 



DESCRirTiON OF THE Disease os ToRArco axd Tomato. 



The appearance of this disease has been described by many 

 investigators, and nearly all have described it in a similar man- 

 ner, bnt more particnlarly with reference to tobacco than to the 

 tomato. The general characteristics of the disease are the same 

 for both plants, bnt some differences are found in extreme cases 

 in its appearance on the tomato, as will be noted from the fol- 

 lowing description:- — 



In the first stages of the disease the leaves of both plants 

 present a mottled appearance, l)cing divided into larger or 

 smaller areas of dark and light green patches, with very regular 

 outlines. At this jioint, however, no unequal sAvelling of the 

 areas is noticeable, but as the disease progresses the darker por- 

 tions grow more rapidly (growing normally), while the light 

 green areas grow very slowly, and in this manner leaf distor- 

 tion is brought about. Tn the tomato the light green areas 

 become yellowish as the disease progresses, and in very badly 

 affected plants become finally purplish-red in color. This col- 

 oration, however, is prol)ably a secondary result of the disease, 

 and is found principally on plants which are exposed to strong 

 light, but does not occur always, as it has been found that 

 sometimes, even in badly affected plants, the disease may reach 

 its maximum intensity without showing any reddish coloration 

 whatever. 



The reddisli {ijipearance is noticeable only on the upper side 

 of the leaf, and extends only through the palisade cells. A dis- 

 cussion of the cause of this coloration will not be taken up in 

 this paper. 



We have un<lei' no conditions ever noticed this coloration on 

 tobacco, but occasionally in the field have seen the affected por- 

 tions of leaves show brown, dead areas of tissue, a condition 

 wdiich may be analogous, but which we have been as yet unable 

 to prove. 



On badly diseased ])laiils of both tobacco and tomato the 

 leaves are iiiucli distorted ntid stiff, and often, especially in the 



