30 MISSOURI BOTANICAL GARDEN BULLETIN 
insures adequate aération, and, at the same time, serves to 
carry off any products which may diffuse into the water from 
the germinating seeds. 
Group XI. The ability of all leguminous plants (clovers, 
beans, etc.) to utilize atmospheric nitrogen is well known. 
This is accomplished through the intermediary of bacteria 
in certain nodules, or tubercular swellings, made by the 
bacteria on the roots of these plants. One of the greatest prob- 
lems in agriculture is to secure and maintain an adequate 
supply of combined nitrogen in the soil, and often the best 
means of accomplishing this is through the nitrogen-fixing 
power of legumes, The conditions favorable for the fixation 
of nitrogen are most important. It is interesting that in the 
presence of rather large quantities of nitrogen in the solu- 
tion culture, nodules do not readily form; but when nitrogen 
is deficient, a profuse development of nodules occurs. More- 
over, in solution cultures in which no combined nitrogen is 
supplied, the plants secure an adequate supply merely 
through the action of the bacteria mentioned. 
Plate 1 is made from a photograph of the experiment with 
~ peas in group II, supplemented by three cultures from group 
3 and these are illustrative of the comparisons to be noted in 
other groups. The photograph was taken ten days after the 
cultures were made, and as growth continues the comparisons 
will become more marked. The following is an enumeration 
of the cultures, the numbers corresponding to those appear- 
ing in the plate: 
1. Calcium salt alone (rts standard Boneentration); 
which permits good growth for a certain time interval— 
about three weeks. 
2. Magnesium salt alone (x4e standard concentration), 
which permits no growth. 
3. Magnesium salt alone (z$s standard concentration), 
which permits little growth. 
4. Combines calcium and magnesium salts as used in 
Nos. 1 and 2, and here the calcium prevents injury from the 
magnesium. 
5. Combines the calcium and magnesium as in No. 4, but 
the latter is increased in strength four times; still the calcium 
prevents any considerable injury. 
6. Combines calcium and magnesium as in No. 4, except 
that there is only one-tenth as much calcium; but its benefi- 
cial effect is still obvious. : : ; 
