Feb., 1923] CLAYTON-TEMPERATURE AND FUSARIUM WILT 73 
chosen. As indicated by this photograph, the minimum for growth is 
9-10 0 C., the optimum about 28° C., and the maximum 37 0 C., when the 
amount of growth is measured by the diameter of the colony. This trial 
was repeated with like results. 
Similar cultures were made to determine the relation of temperature to 
size and septation of spores, the detailed results of which are not pertinent 
to this discussion. It was found, however, that, even when a single-spore 
strain of the fungus was used, there were marked differences in the average 
size of the spores as well as in the number of septa in the spores obtained 
from cultures grown at different temperatures. 
Temperature Responses of the Normal Host 
Two commercial varieties of tomato, Mangus and Chalk’s Early Jewel, 
both susceptible to the wilt disease, were used in these studies. In each 
experiment uninoculated plants were grown as controls under the same 
conditions as the inoculated plants. These controls afforded an opportunity 
to study the growth of the host at different soil temperatures. It was 
found that the temperature range which, in sterilized soil under greenhouse 
conditions, proved most favorable for a vigorous development of these 
varieties was from 24 0 to 31 0 C. This range includes the temperature for 
the optimum development of the fungus (28° C.). The growth of the 
uninoculated plants is illustrated in Plate IX, C, a photograph taken one 
month after the plants had been transplanted at soil tempera Lures of 19 0 , 
22 0 , 24 0 , 28°, 31 0 , 33 0 , and 35 0 C. respectively. As stated above, the 
plants grew most vigorously at temperatures of 24 0 to 31 0 C. and somewhat 
less vigorously at 33 0 C., while at 35 0 they lived but did not increase appre¬ 
ciably in size. In the cooler soil, growth decreased gradually from 24 0 to 
19 0 C. and below. 
Symptoms of the Disease 
General Symptoms. The Fusarium wilt of the tomato as produced in 
the greenhouse at Madison was characterized by a progressive wilting of 
the leaves, often accompanied or preceded by a yellowing of the affected 
leaves. The wilting was sudden and permanent and developed most 
rapidly during bright, sunny weather, with little or no recovery during the 
night. The browning of the infected bundles could readily be seen in the 
cut stems. The roots appeared normal externally, though the bundles were 
browned as in the stems. 
In well-developed plants three to four weeks old, the first external 
evidence of the disease was always the wilting of a lower leaf, this leaf being 
the first one supplied by the infected bundle or bundles. Frequently, one 
side of such a leaf wilted and the other side remained healthy for a time. 
In such instances, a cross section of the leaf petiole showed discoloration of 
the bundles on the wilted side only. The disease appeared next in other 
