EXPERIMENTAL STUDY. 51 
EXPERIMENTS WITH COWPEAS. 
The four pots were planted to cowpeas April12z. On April 22 plants 
were up in Nos. 1, 2, and 3, and on the 25th in No. 4. On May 15 
the plants were all thrifty, and the following shows the growths on that 
date and on June 14: 
GROWTH ON MAY 15. GROWTH ON JUNF 14. 
Centimeters. Centimeters. 
LF DURST iy ls i ag re PAPAL Ne ete, 2 ee AES oe ee eter 34 
eg Oe ek ee Pe AN tee PEs hw es ie ee ee Bee a ee ee 
Were ee Ste ee Ne a. be en oo Bea Nas oe oS hr DIG Se ea ee ee 34 
NaS See fk Bre sobre _ot 5g) a Eh ents So PR 19 
Nos. 1, 2, and 3 were very much alike in general thriftiness and 
were of a uniform dark-green color. No. 4 was spindling and of a 
light-green color. On June 26, one and one-half months from 
planting, a photograph was taken of the four pots. (See Pl. III, 
fig. 2.) No.1 is the check; No. 2, CaO, as sulphate, 9.8 per cent; No. 
3, CaO, as sulphate, 0.8 per cent; MgO, as carbonate, 0.2 per cent; 
No. 4, CaO, as sulphate, 0.2 per cent: MgO, as carbonate, 0.68 per 
cent. 
It will be noticed that the addition of an excess of calcium sulphate 
did not cause a deterrent effect in the presence of 0.144 of .soluble 
magnesia, nor did the addition of more magnesia in No. 3 produce a 
favorable effect over the check, showing that the magnesia already 
present was sufficient for the plants grown. As shown by the check, 
No. 1, 0.14 per cent of soluble lime was also sufficient for the direct 
needs of the plant. In No. 4, with the addition of 0.68 per cent of 
magnesium carbonate and 0.2 per cent of calcium sulphate, the noxious 
influence of the former is apparent. While not sufficient to cause the 
death of the plants, it hindered their growth to such an extent as to 
preclude the possibility of the production of a profitable crop. 
While liming may be protitably carried on for bettering the physical 
condition of soil, the correction of acidity, and other reasons, it may 
also in certain cases be beneficial from a physiological standpoint. 
The need for it may be surmised from an analysis of the soil. Though 
only the soluble lime and magnesia affect the immediate growth of 
plants in a given soil, it is apparent that where one element is in great 
excess of the other it will naturally be present in larger proportion in 
the soil solution. 
When the magnesia content of the soil is large and the application 
of calcium sulphate is expensive, the determination of the soluble salts 
would be advisable before liming. However, in that case the applica- 
tion of lime, though lessened, would be of only temporary advantage, 
as successive applications would be needed. In this connection, it 
would be of value to construct a table showing the curve of solubility 
of lime and magnesium salts in the same culture medium or solution. 
