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PACIFIC SCIENCE, Vol. I, July, 1947 
is no sharp curtailment of growth even in 
the cans having over 3,000 ppm of soil 
arsenic. Although the tomatoes growing in 
the cans at the upper concentration levels 
were slightly inferior in size to those in the 
lower levels, they were otherwise normal in 
every respect. They showed no premature 
drying or yellowing of leaves, their roots 
were as extensive as the others, and yet the 
arsenic levels in the plant tissues were very 
high. In Can 24, the first crop of plants 
appeared perfectly normal with good color, 
despite the fact that the crop contained 76.1 
ppm of arsenic. Like those in the red soil, 
though to a lesser degree, later crops of 
tomatoes in black soil failed to extract as 
much arsenic from the high arsenic soil as 
did the first crop. 
Sudan Grass: Red Soil .—Sudan grass 
plants, as shown in Table 9 and Figure 3, 
grew uniformly well in all cans up to Can 
10, in which the arsenic content of the soil 
was 104 ppm. There is no suggestion of 
stimulation in the cultures having lower con¬ 
centrations of arsenic. At the higher levels 
of soil arsenic, Sudan grass extracted sub¬ 
stantially higher amounts of the poison than 
did the tomato. The first crop of grass ab¬ 
sorbed larger quantities of arsenic at the 
higher levels than did later crops. In fact, 
each succeeding crop of Sudan absorbed less 
and less arsenic from the soil, but in each 
crop the depression of growth occurred at 
the same level of soil arsenic, a fact again 
pointing to the idea that the actual arsenic 
level in the plant is not causal, though it is 
Fig. 3. Green weights and arsenic content of Sudan grass grown in red 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 9.) 
