[Vor. 4 
202 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
began to drop off, presumably due to excessive transpiration, 
until only a few remained at the top. These later became 
chlorotic, but they were not uniformly colored, being speckled 
with green areas. Whether or not this can be interpreted 
as a recurrence of the disease or merely an unmasking of the 
formerly diseased areas cannot be stated positively, but it 
probably is the latter. The plant died shortly after this last 
observation was made. The case of this potato plant is, of 
course, but a single instance, but it is entirely in accord with 
the other observations. 
No record was kept of the amount of water supplied to the 
plants in the various experiments. They were all watered ac- 
cording to their normal needs under greenhouse conditions. 
The greenhouse observations substantiate those on the plot. 
When the tomatoes on the plot showed no mosaic, the tobacco 
and some of the cucurbits were greatly mottled. 
It therefore not only seems that individual plants exhibit 
an optimum for the mosaic in accordance with the optimum of 
their growth, but that there also may be a maximum beyond 
which little or no mosaic is manifested. If this is true we 
should also find a minimum, and some very interesting obser- 
vations have been made in this direction. In a recent article, 
Brierley (716) reports recovery of tomato plants from mosaic. 
Inoculations were made by him, but he states that ‘‘unfor- 
tunately the plant was killed outright by frost ten days later, 
at that time showing no sign of disease." From this we would 
conclude that the plant was kept in a comparatively cool place. 
This same phenomenon was observed in tobacco plants kept 
at 45° Е., as has been stated above and shown in pl. 14. 
Another observation was made in the fall of 1916. Plate 15, 
fig. 1, shows two plants (b and с) which are the same age, 
the one perfectly healthy, the other presumably affected with 
mosaic. On November 20 plant b was removed to a green- 
house to which no heat was supplied. The photograph of 
plant а was taken on December 13, 1916, after which 
plant b was placed in a greenhouse maintained at 65-75? Е. 
in order to note a probable recurrence of the disease. The 
plant, however, remained healthy and fruited normally. No 
