Feb. 7,1916 
Boron 
887 
control yield, more than that obtained from the unmanured control plot. 
The yellowing of the leaves is an unmistakable sign of injury, although in 
some cases the plant can recover, or at least is not sufficiently injured to 
cause a reduction in the yield. 
Haselhoff (7) states that the action of boron is more marked on beans 
than on oats or com, and that it can be seen when small amounts of boron 
are present in the soil and when no action injurious to plant growth is 
evident. He says further that small amounts of boron stimulate the 
growth of beans and corn, while large amounts produce injury. In his 
experiments beans absorbed boron in proportion to the amount present 
in the soil up to a certain limit. The plants examined by Haselhoff con¬ 
tained from 0.04 to 0.17 per cent of boron, which is more than was found 
in these experiments, with the exception of the plants grown at Orlando, 
Fla. (Table VII). He suggests that for safety the amount of boron in 
the soil be less than 0.0001 per cent. According to Brenchley (5), peas 
are stimulated by relatively high concentrations of boric acid, but with 
larger applications of boric acid the toxic action was well marked on the 
leaves, which tend to become brown and to die in a characteristic manner. 
There is some evidence in the literature to indicate that small amounts 
of boron stimulate plant growth. Brenchley (5) states that below a cer¬ 
tain dilution boron tends to produce stronger roots and shoots. Large 
amounts of boron are known to be toxic to practically all plants, with the 
exception of certain fungi. 
In these experiments, where in most cases more boron was added than 
was necessary to act as a larvidde, no stimulating action was noted. On 
the contrary, an injurious action was seen with leguminous plants, which 
became yellow and did not show a good stand. Tomatoes, beets, let¬ 
tuce, potatoes, radishes, corn, oats, and wheat appeared normal when 
grown in the presence of amounts of boron which produced injury to 
leguminous plants. When borax is added to manure at the rate of 0.62 
pound to each 8 bushels and the manure is applied to the soil at the rate 
of 15 tons per acre, 0.0011 per cent of boron is added to the soil. This 
quantity of boron may injure leguminous plants, but did not injure the 
other plants tested, although no stimulation was noted. If the borax- 
treated manure is mixed with untreated manure, as would be done in 
many cases, since it is necessary to treat manure with borax to destroy 
fly larvae during only a portion of the year, it is possible that the per¬ 
centage of boron would be sufficiently reduced to bring about a stimu¬ 
lating action on plant growth. 
In connection with the stimulating action of boron, it may be men¬ 
tioned that nitrites and nitrates were detected in three or four borax- 
treated manure piles at New Orleans (6, p. 19), while the corresponding 
control piles contained no nitrites or nitrates, and several soils fertilized 
with borax manure have shown more nitrates than the check soils. A 
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