Tne, a See A 
ALLARD: MOSAIC DISEASE OF TOBACCO 449 
mosaic shown by the single control progeny it seems fair to ask if 
Jensen’s experiments have been extended sufficiently to warrant 
final generalizations as to the greater resistance of progenies of 
healthy over mosaic parents. 
Delacroix (49), in 1906, reviewed rather fully previous investi- 
gations of the mosaic disease of tobacco. 
As a means of preventing the disease, he advises making seed 
beds in new soil which has not previously grown tobacco. He also 
recommends crop rotation in the field, and cautions against the 
use of insufficiently rotted organic manure, and the choice of soils 
naturally too wet. 
At the same time, Delacroix discusses a leaf-spot disease 
which he calls ‘“‘la maladie des taches blanches” to distinguish it 
from a spot disease which he has previcusly described as “‘rouille 
blanche.”” He is convinced that the disease termed ‘‘mal del 
mosaico”’ by Comes and F. Pirazzoli is identical with his “maladie 
des taches blanches.’”’ Delacroix is not quite certain as to the 
relationship of ‘‘rouille blanche’ and the “maladie des taches 
blanches.”’ 
Baur (50), in 1906, mentions the mosaic disease of tobacco in 
connection with a discussion of infectious chlorosis of the Malva- 
ceae. He is inclined to believe that they are not essentially 
different in some respects. It is mentioned that the former is, 
however, transferred by other means than by grafting, and that 
the virus of mosaic is more stable, since the principle of infectious 
chlorosis can exist only within the living cells of the Malvaceae. 
In 1907 Hunger (51) expressed his views concerning the effects 
of shade as a preventive of mosaic in tobacco. In a test of two 
plots with Deli tobacco, one shaded, and another unshaded as a 
control, he states that only 8 per cent of the plants became mosaic 
under shade, while 44 per cent became mosaic in the sun. He 
considers this a striking confirmation of. Sturgis’s results in Con- 
necticut. — 
In explanation of these results, Hunger considers that shade 
so regulates the various physiological activities of the plant that 
the phytotoxin of mosaic is not generated. He contends that 
mosaic arises only when unfavorable external conditions stimulate 
the secretion of this specific toxin, which once formed has the 
