25 
and others seem to depend upon changes in the weather.’ Solely a 
surplus amount of water in the soil, involving a deficiency of root aera- 
tion, does not produce the mosaic disease, as the writer observed. In 
a field one corner of which was continuously moist, the plants were of 
a uniformly yellowish-green all over, and they were only about half the 
height of the healthy plants, but there was no trace of symptoms of 
mosaic disease visible. 
The diminished amount of chlorophyll in mosaic diseased plants, 
leading to a diminished production of organic matter, soon shows its 
effect in the more or less retarded development of the whole plant. 
There is also less coagulable albumin and less acid in the leaves of the 
diseased plants than in those of healthy ones of about equal age. The 
juices were titrated with one-tenth normal soda solution and the acid 
calculated as malic acid. 
The following amounts of malic acid were found in a diseased and in 
a healthy plant: 
Diseased | Healthy 
plant. plant. 
Per cent.| Per cent. 
SETI EN aN ae eas cata Cenc a Tesrav as ate ra rav cla ale a ature ve Oates ava gn imtiainie lalctaire aja la tarelarararava otuls atmithetaisielel sarsiaiatare 0. 033 ON033 
JUG UAC OR NEE PER SS Gee SEE Oe AE OE SEIS CIDER SCRE hey RRR er ae esha On en ge eee SRE . 048 . 105 
NRA TN ea Oa eet hee set eret care ekeray ete ote rate rales evaie terete ai Mere ay Syaovias on eeielsete eine stenoeioe Gann . 210 a Pate 
a After removal of midrib and large side ribs. 
The relative amounts of oxidizing enzyms also are different in dis- 
eased and healthy leaves. The observations of the writer agree essen- 
tially with those of Woods.? Not only the midrib and the pith, but 
even the dead spots of the diseased leaves contain very much oxidase, 
while the lamina contains much more peroxidase than that of healthy 
leaves. The writer had occasion to observe tobacco fields, just before 
harvesting time, in Connecticut and Massachusetts, and was surprised 
at the great differences in the extent of the disease even on neighboring 
fields. Some planters entertain the belief that a too extensive use of 
mineral fertilizers favors the disease, and, indeed, those fields had 
the least number of diseased plants which had received chiefly organic 
manure. Mr. Du Bon, of Poquonock, Conn., whose crop of Habana 
'One cause may be an insufficient distribution of the manuring material. A 
tobacco grower at Poquonock set his plants in a field in which one inch of earth 
covered the cotton-seed meal employed as manure, the latter not being uniformly 
mixed witb the earth. On further development more than 50 per cent proved calico 
plants. 
2Paper read before the American Association for the Advancement of Science at 
Columbus, Ohio, August, 1899. Other papers on this disease have been published 
by Dr. Wm. C. Sturgis, Conn. Agr. Exp. Sta. Report for 1898; further by Adolf 
Mayer, Landw. Vers. Stat., vol. 32 (1886); by Beijerinck, and by J wanowski, Centr. 
Bakt., vol. 5. 
