168 
PACIFIC SCIENCE, Vol. I, July, 1947 
/ Z 3 4 £ & 7 6 9 70 77 7Z 73 74- 7& /& /7 76 79 ZO Z7 ZZ Z3> Z4- 
30/L - COL TL/RB CA A/ /VOM 3 BR 
Fig. 5. Green weights and arsenic content of bean plants 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 11.) 
two. In the red soil, the arsenic concentra¬ 
tions which were toxic to Sudan grass, bean, 
and tomato were approximately 110, 250, 
and 550 ppm, respectively. In pounds per 
acre foot of dried soil, these figures become 
roughly 220, 500, and 1,100 pounds, respec¬ 
tively. 
Perhaps the fact that Sudan grass is a vig¬ 
orous feeder especially of fixed phosphorus 
in such soils is related to its greater sensitiv¬ 
ity to soil arsenic, which probably is sim¬ 
ilarly fixed. Such an observation has sup¬ 
port in the data presented for red soils, 
which demonstrate that Sudan grass ex¬ 
tracted higher levels of arsenic from Cans 
10 to 16 than did either of the other two 
plants. Both tomatoes and beans when 
grown on Hawaiian soils are fertilized 
heavily with phosphates in order to obtain 
good growth. The large grasses, however, 
seem to be able to take their phosphorus even 
though it is highly fixed. 
It is doubtful whether arsenic which is 
applied to soils as trivalent arsenic remains 
trivalent after it has been in the soil for 
some time. Although no direct pertinent 
data are available from this study, indirect 
data may be obtained from the arsenic levels 
attained by the Sudan grass and tomato 
plants growing on the black soil. Tomato 
plants in black soil (Can 22) which were 
apparently normal contained up to 104 ppm 
of arsenic. Sudan grass plants in black soil 
in Cans 21 and 22 contained between 30 
