THE MOSAIC DISEASE OF TOBACCO. 7 



purplish yellow, or white-flowered species of Nicotiana observed by 

 the writer have shown this phenomenon in diseased plants. A few 

 of the more common species observed in this connection may be 

 mentioned here : 



Nicotiana silvestris (blossoms white). 



N. rustica (blossoms greenish yellow). 



A 7 , longiflora (blossoms purplish). 



N. alata (blossoms white). 



N. langsdorfli (white and yellow flowered forms). 



N. paniculata (blossoms greenish). 



The red-flowered forms of Nicotiana forgetiana have not been 

 modified by the disease. 



The various manifestations in the intensity and unequal distri- 

 bution of color in the blossoms of mosaic tobacco plants bear a strik- 

 ing resemblance to the mottled color of peaches produced by trees 

 affected with peach yellows. Speaking of the mottled color of 

 peaches produced by diseased trees, Smith x says : 



The amount of color appears to depend somewhat upon variety. Sometimes 

 there is comparatively little crimson spotting, and again, it is a very marked 

 feature, the skin being almost purple and the flesh of the deepest crimson, 

 even in pure white varieties. In an experience covering four years and includ- 

 ing a great many thousand trees diseased by yellows, I have never known but 

 one in which there was entire absence of red spotting in the fruit. This tree 

 bore premature insipid peaches and the characteristic shoots. 



Farther on he says : 



In many cases the red-spotted, prematurely ripened fruits are the first indi- 

 cations of disease, or at least the first symptoms striking enough to attract 

 general attention. They are very often borne exclusively upon one or two limbs 

 of otherwise healthy-looking trees. These limbs are not different in appear- 

 ance from the rest of the tree. They bear vigorous shoots and full-grown, 

 smooth, dark-green foliage; often, also, green, half-grown fruits, which after- 

 wards ripen in a normal manner. There is no indication of disease except in 

 the fruit, which, in color and size, contrasts strikingly with the fine green foliage 

 and the normal, immature fruit. 



LOCAL AND GENERAL MANIFESTATIONS OF THE DISEASE. 



It is a matter of common observation that obvious symptoms of 

 the mosaic disease do not necessarily appear in all parts of a plant 

 simultaneously. In an affected plant individual leaves, branches, or 

 blossoms of the same flower cluster may show localized symptoms of 

 the disease. A leaf may appear quite healthy and normal except for 

 a few small isolated blisters. Branches healthy in appearance some- 

 times grow close beside those showing the most pronounced symp- 

 toms. Likewise, in a flower head, blossoms normal in color are often 

 intermingled with those showing extreme phases of mottling. 



1 Smith, Erwin F. Additional evidence of the communicability of peach yellows and 

 peach rosette. U. S. Department of Agriculture, Division of Vegetable Pathology, Bul- 

 letin 1, 1891, p. 12-13. 



