Arsenic Toxicity Studies— Clements and Munson 
163 
Fig. 2. Green weights and arsenic content of tomato plants grown in black soil with arsenic content 
ranging from 15 ppm (Can 1) to 3,014 ppm (Can 24) of As 2 0 3 . The difference in levels of the two 
green-weight curves is due to the season in which the plants were grown and is not related to treat¬ 
ment. (For As 2 0 3 increments, see Table 8.) 
from 3 ppm to 4 ppm. From higher levels 
of soil arsenic the plant absorbs increasing 
amounts of the poison, and this heavier ab¬ 
sorption is reflected in greatly reduced 
growth. 
Although the level of soil arsenic which 
might be described as critical for the tomato 
is the same for the later crops of plants as 
it is for the first crop, there is a striking dif¬ 
ference in the amounts of arsenic absorbed 
by the later crops. Thus, the first crop in 
Can 18 contained about 52 ppm of arsenic, 
while the later crops in Can 18 absorbed 
about one tenth as much. A very much 
higher level of soil arsenic was necessary for 
the later crops to absorb 52 ppm. Two pos¬ 
sible hypotheses suggest themselves. First, 
the fixation of arsenic by the soil may be a 
function not only of the nature of the soil 
but of time. Second, the soluble arsenic 
level of the soil may be reduced sufficiently 
by the first crop to reduce its absorption by * 
later crops. However, the fact that growth 
in the first series as well as that in the later 
series is reduced in the same cultures does 
not lend support to the latter hypothesis. 
Tomato: Black Soil .—The growth of 
young tomato plants in black soil, as shown 
in Table 8 and Figure 2, is very much better 
than it is in the red soil. The black soil is 
not only very fertile, but it possesses physical 
qualities which make it a better soil for pot 
work. The most striking contrast between 
the two soils is that in the black soil there 
