78 MASS. EXPERIMENT STATION BULLETIN 175. 



Both substances, virus and anti-virus, may be increased by external factors or 

 conditions. In the first instance the plants become diseased with the mosaic 

 disease; in the latter an immunity against the disease is brought about. Decrease 

 in intensity and cure occur if the virus formation ceases or stops, while at the same 

 time the formation of an anti- virus is taking place normally or is increased. ^ 



A discussion of Lodewijks' work is to be found later in this paper. 



Allard^ in a recent work on the disease states that from the results of 

 his experiments he is of the opinion that the trouble is not primarily 

 ph3''siological but is parasitic in nature, but he is unable to throw any 

 light on the nature of the parasite, and in spite of the conclusions drawn by 

 him, none of his results, at least in so far as the writer is able to judge, has 

 in any way weakened the theory that the trouble may be physiological in 

 nature; and some of his results, from the writer's point of view, seem to 

 substantiate this idea of a physiological agency. Two points of great 

 interest are brought out by him, viz., the mosaic as affecting the color 

 of the corolla by blotching, etc., and the carrying of the disease by certain 

 aphids. These points have not been noted before. In the following 

 pages some of his work mU be taken up in detail in so far as it seems to 

 bear out or refute work done by the writer. 



It may be seen from the foregoing r^sum^ that the theory that the disease 

 is physiological in character has been in the past pretty generally accepted,, 

 but the identification of the ultimate causes producing the symptoms 

 varies widely with the different investigators. The writer's conclusions- 

 with regard to this point are taken up later in this paper. 



Names. 



By right of priority the term "mosaic" is the one which should be 

 applied to this disease. It has, however, many local names, and these 

 sometimes are applied differently to the different manifestations of the 

 sjTnptoms; among them may be mentioned the following: "calico," 

 "brindle," "mongrel," "mottle-top," "string leaf," "frenching," etc. 

 Other terms have also been used, but they do not in aU cases apply to the 

 "mosaic" alone, hence they are here omitted. The term "infectious 

 chlorosis " as suggested by Clinton is perhaps best descriptive of diseases 

 of this general character, with "mosaic" as a specific type under this 

 division, there being many other infectious, clilorotic diseases of plants 

 quite distinct from the mosaic type. 



Description op the Mosaic Disease of Tobacco. 



Descriptions of the mosaic disease of tobacco have been repeatedly 

 presented, and the disease itself is so well known that there is little need 

 of repetition at this point, but a brief r^sum^ of the salient characteristics 



» Translation from abstract of Lodewijks' paper in Bot. Centralbl., 114-518 (1910). 

 ' Allard, H. A.: Mosaic Disease of Tobacco. U. S. D. A., n. s., Bur. Plant Ind., Bui. No. 40 

 (1914). 



