Dec., 1923] 
SHERWOOD — FUSARIUM WILT OF TOMATO 
549 
The sterilization process caused greater changes in the reaction of the 
medium than in experiment 1. This was especially marked in flasks 8, 9, 
and 10, which contained the most alkaline medium. It was also observed 
that the medium in these flasks had considerably more color than the others. 
While the heaviest production of mycelium occurred in the media testing 
pH 7.2, 7.6, and 8.0, growth was accompanied as before with marked 
changes toward greater acidity. Growth at pH 2.2 was very light in this 
case, and, as no germination occurred at pH 1.8 in experiment 1, it appears 
that under the conditions of the experiments the limiting hydrogen-ion 
concentration for spore germination is about pH 2.0. As far as mycelial 
growth is concerned, the results of the two experiments are not very consis¬ 
tent; but, as growth in the duplicate flasks was quite uniform in all cases, 
the results may be partially explained as being due to different nutritive 
relations caused by the sterilization process. 
Discussion and Conclusions 
That soil reaction has a marked influence on the development of the 
Fusarium wilt of tomato seedlings is clearly shown by the experimental 
data. The percentage of diseased plants was in all cases greatest in the most 
acid soils, and always decreased quite uniformly as neutrality was ap¬ 
proached. These results have been consistent with both the sandy-loam 
and the silt-loam soils. The amount of infection has, however, shown con¬ 
siderable variation under the conditions of the several experiments. It is 
apparent, therefore, that the total amount of disease which developed in 
each experiment depended upon conditions more influential than the reac¬ 
tion of the soil. Thus, in the sandy-loam soil having a reaction of pH 6.8 
in each experiment, the total percentage of infected plants in experiment 1 
was 41; in experiment 2, 60; and experiment 4, 42. Likewise, in the silt- 
loam soil having a reaction of pH 6.4 in each experiment, the total percentage 
of infected plants in experiment 1 was 24; in experiment 2, 48; in experi¬ 
ment 3, 60; and experiment 4, 66. 
The amount of disease developing in the two types of soils of the same 
hydrogen-ion concentration under the conditions of the same experiment 
also varies to a considerable extent. In experiment 1, for example, in soils 
having a reaction of pH 6.2, 55.3 percent of the plants in the sandy-loam 
soil became infected, of which 38.8 percent died, while in the silt soil 30 
percent became infected and 13 percent died. On the other hand, in experi¬ 
ment 2 in soils testing pH 5.8, the corresponding figures are 73.4 percent and 
45.0 percent in the sandy soil, and 75 percent and 46 percent in the silt soil. 
A difference may be expected in the disease development in two soils as 
widely different as a sandy loam and a heavy silt loam. Such factors as 
supply of plant food, aeration, and organic-matter content, no doubt, 
either directly or indirectly may play some part in influencing results. 
It may be observed that it was necessary to add more calcium carbonate 
