444 Wisconsin Academy of Sciences, Arts, and Letters . 
temperature, led to the clear definition of the question whether or 
not soil temperature may be the limiting factor with this tomato- 
wilt disease. Dr. E. E. Clayton, as a graduate student, undertook 
to determine the facts, and the following summary is taken from 
his full report, which is now awaiting publication. To begin with, 
he made trials by the agar-plate pure-culture method to determine 
the influence of temperature upon the growth of the fungus. The 
results, which are shown in Plate XXXIII, figure 3, made it clear 
that the parasite is rather sharply inhibited in its development at 
both low and high temperatures. Trial culture of the host in non- 
inf ested soil held at different temperatures,, the air temperature 
being the same for all, showed that the tomato plant has a somewhat 
wider range of temperature toleration than has the Fusarium 
(PI. XXXIII, fig. 1). It is noteworthy, however, that the optimum 
temperature alike for the development of the fungus and of the 
host under the conditions of these trials is practically the same, 
viz., about 28° C. It is of especial interest now to learn the re¬ 
sults secured by Clayton when tomato plants were grown in 
Fusarium-infested soil held experimentally at different tempera¬ 
tures ranging from the lower to the higher limits of the heat toler¬ 
ance of tomato roots. These are illustrated by photograph in Plate 
XXXIII, figure 2. 
From these data it is evident that the development of the dis¬ 
ease is definitely and quite sharply conditioned upon favorable 
temperature. It is noteworthy also that the soil temperature which 
in general seems most favorable for both the tomato and its parasite, 
28° C., is approximately that at which the disease appears first 
and proceeds most rapidly to the destruction of the host plant. It 
is of further interest to note that, although the lower limit or 
critical point for the inception of the disease, 19°-20° C., is nearly 
the same as for the two related Fusarium diseases of cabbage and 
of flax, it is actually sufficiently higher (cabbage and flax be¬ 
ing about 16°-17° C.) to correspond in a general way with the 
difference in temperature relations of the respective hosts, the 
tomato being favored by distinctly higher temperatures than are 
cabbage and flax. In this connection we may recall that the temper- 
ture relations of the three Fusarium parasites are practically 
identical. Quite as striking as the sharp delimitation of the dis¬ 
ease by soil temperature at the lower point is that at the upper 
(Plate XXXIII, fig. 2), where it seems that the tomato can live at 
soil temperatures well beyond the range of attack of the parasite. 
