120 
IOWA ACADEMY OF SCIENCE 
appeared and has allowed the clover to grov/ in a normal manner. The only- 
other explanation is that the plant food has become more available, but this is 
easily disproved. Pot 39 received soluble plant food in abundance, undoubtedly 
having a great deal more than pot 71 could have, taut pot 39 is only a shade 
better than pot 44 and not nearly up to pot 71. Therefore it is not a plant 
food question. This was not an isolated case, but the same occurrence hap- 
pened several times. The soil, when allowed to lie in the greenhouse and dry 
for several months, invariably became much better suited for the growth of 
clover. This certainly suggests the presence of a toxin in the soil. 
The methods pursued by the Bureau of Soils to determine the presence of a 
toxin were not applicable -in this case, for clover does not submit to the special 
treatment required, namely, growing in w^ater cultures in bottles. An approach 
to their methods was made by proceeding as follows: Soil sufficient to fill a pot 
was spread out one inch deep in a large sieve over which a piece of muslin 
had been spread. Water was leached through this until twice the weight of 
the soil had run through. The soil was then dried until it came to optimum 
water content, carefully worked and treated for several days to destroy any 
lumps, and then packed into the pot. The leached water was applied to the 
soil for another pot. This was allowed to dry and was then put into optimum 
physical condition and packed into the pot. It would seem that if this soil 
contained a soluble poisonous substance that retarded the growth of the clover, 
that the soil would be better for washing. It would also seem that if this 
extract containing the toxin were transferred to another sample of this soil, 
that it v/ould be there concentrated and still further hinder the growth of the 
clover. Of course, this extract will carry other things beside the toxin, among 
which is considerable plant food, but if the toxin overbalances the effect of 
these things in the original soil, why would it not have the same effect when 
applied to a new pot of soil? 
In the following series, pot 224 was filled with soil which had been leached, 
and this leaching, or extract, was added to the soil in pot 222. In the same 
way the leaching from pot 225 was added to pot 223. The series was planted 
October 19, 1906, and it was harvested ninety-one days later. The data secured 
is here given. 
TOXIN EXTRACT SERIES 
II 
Treatment 
Green 
weight g 
No. 
plants 
Relative 
weight 
Average 
200 
Check - — 
4.1 
10 
96 
201 
Check 
4.4 
10 
103 
100 
222 
Extract added 
4.0 
10 
94 
223 
Extract added 
5.9 
10 
139 
116 
224 
Leached — _ _ 
5.45 
10 
128 
225 
Leached __ 
4.9 
10 
113 
120 
The data shows that the pots which were leached have an average gain of 
20 per cent, showing benefit from the. process. But the effect of adding the 
extract to the soil is uncertain. One of the pots shows a slight decrease in the 
grov/th of the clover, and the other one a large gain. Therefore it cannot be 
claimed that the presence of a toxin was proved by the experiment, but the 
results certainly suggest that there was a toxin in the soil. Undoubtedly the 
method is crude, and it is not certain that reliable results could be obtained 
by it, no matter how large the number of duplicates. 
