June, 1913,] The Mosaic Disease of the Tomato. 165 



But he states that there is evidence that rapid growth, caused 

 by excessive nitrogenous manure or too high a temperature, is 

 favorable to it. This latter statement seems to correspond with 

 observations made by the writer on the appearance of some 

 cases of tomato mosaic under glass. Woods (1902), does not 

 explain why nitrogenous fertilizers should act in this manner; 

 the plants are really in need of reserve nitrogenous compounds, 

 as will be seen later. He says, however, (p 23), "It is probably 

 connected, however, with the manufacture of reserve nitrogen 

 by the cells and its distribution to the rapidly growing parts. " 

 He thinks that tobacco mosaic is especially liable when moist 

 cloudy weather, stimulating rapid growth, is followed by hot, dry 

 weather, checking growth and causing the soil to bake, so that 

 cultivation is apt to injure the root system. 



He carried out inoculation experiments along the same lines 

 as other investigators, showing that this disease is infectious. 

 He performed other experiments however, to prove that mosaic 

 disease could be prodiiced at will without employing the juice 

 of diseased or healthy plants. He was able to produce mosaic 

 disease on tomato plants by severally pruning them. Pot-bound 

 tobacco plants were selected and after they had been cut back, 

 (allowing two or three lower leaves to remain), they were sub- 

 mitted to high temperature and copious watering. The rapidly 

 developing shoots became mottled and often distorted. Mosaic 

 disease appeared in plants which were simply punctured with 

 a steril scalped and in other cases where a piece of healthy leaf 

 was inserted. Juice of diseased plants, boiled and double boiled 

 when injected into the terminal bud, or poured around the roots 

 caused the appearance of the disease. Woods (1899, p. 753) 

 says, "It seems plausible that in rapid, poorly nourished growth 

 many of the cells were unable to develop their normal amount 

 of chlorophyll by reason of the excessive development of oxidizing 

 enzymes. " 



Oxidizing Enzymes. — Woods states (1902, p. 23), "The disease 

 is not due to parasites of any kind, but is the result of defective 

 nutrition of the young dividing and rapidly growing cells, due to a 

 lack of elaborated nitrogenous reserve food accompanied by an 

 abnormal increase in activity of oxidizing enzyme in the diseased 

 cells." According to Woods (1902), this excess of oxidases in 

 turn inhibits diastatic activity so that starch accumulates in 

 diseased cells in abnormal quantities. The resulting imperfect 

 translocation may be demonstrated by the application of iodine 

 at different hours during a day. By this means a striking difference 

 between the normal and the abnormal tissue may be demon- 

 strated. Suzuki (1902) arrives at similar conclusions, in the study 

 of his mulberry disease; he confirmed Woods' experiments, showing 

 that it was brought on by excessive pruning and that there was an 



