620 INSECTS AFFECTING VEGETATION 



lime and then diluting it with water to 10 gallons. (S. Car. E. S. 

 B. 41.) 



TOBACCO DISEASES. 



The Mosaic Disease of Tobacco. The mosaic disease, or 

 Trenching, of tobacco, locally known in Connecticut as calico, is 

 one of unusual interest. The diseased plants exhibit such a mot- 

 tled appearance of the leaves, due to the alternating a'reas of darker 

 green and yellowish green in them, as to make the appearance of 

 the plants very striking. The leaves are veritable mosaics; as such 

 they catch and hold the interest of the observer. Certain plants 

 will exhibit these characteristics and color markings while others 

 near them have the normal, uniform green color. In the tobacco 

 field, as most will recall, plants with abnormal color are quite fre- 

 quent in unfavorable soil situations and especially around wet 

 areas. This class of situations is however by no means the only 

 one ; no particular specifications may be made to apply generally in 

 this respect. The mosaic disease occurs in practically all tobacco 

 areas of this state and of the United States and under favorable soil 

 conditions; indeed the disease is general throughout the tobacco 

 growing districts of Europe and Asia as well. Along with the mot- 

 tled, or mosaic appearance of the leaves we may have distortions of 

 the leaves due to the unequal rate of expansion in the more healthy 

 and in the diseased areas of the leaves. (Ohio E. S. B. 156.) 



Possibly no other type of plant disease has so long resisted the 

 efforts of investigators to discover the cause producing it. It seems 

 now that we must class the mosaic disease of tobacco, the yellows 

 of the peach, peach rosette, the mosaic disease of tomatoes and the 

 mosaic disease of forcing house cucumbers, which the writer has re- 

 cently investigated at Ashtabula, Ohio, in one and the same group of 

 maladies. To discover the actual cause, or causes of these diseases 

 has long been the aim of students of plant pathology. In recent 

 years decided progress appears to have been made; but as yet the 

 final word is to be said on this matter of cause. Mayer early made 

 a careful study of the disease. He showed that the disease is trans- 

 mitted by inoculation and concluded that it must be the work of 

 bacteria. In 1898 Beijerinck made a decided contribution. He 

 showed that the juice of diseased plants, filtered through porcelain 

 filters, yet retained the power of producing the disease when a small 

 drop of it was injected into a growing bud -of a healthy plant; he 

 also found that diseased tissue kept these infectious qualities even 

 after drying and retained its injurious properties in the soil during 

 the winter; he further demonstrated that the soil around the roots 

 of diseased plants may affect the roots of healthy plants. Studies 

 of the disease have been made in our country by Sturgis and by 

 Woods. The last named publication will be of very great value to 

 any one who wishes to study the conditions surrounding the pro- 

 duction of the mosaic disease in tobacco. Just as in a sense Beije- 

 rinck was the discoverer of what he called a living fluid contagium 

 which he regarded as the cause of the disease, Woods was able to go 

 further and ascertain the presence of certain enzyms in the plants 



