28 ABSORPTION AND EXCRETION OF SALTS BY ROOTS. 
entirely overcomes the harmful effect on root growth of magnesium 
alone. The duration of cultures was eight days; temperature at 
the beginning 21.5°, at the end 19.5°. 
The influence of calcium on root development in the cultures of 
this series was extremely interesting. In experiment C, as in experi- 
ment 5, calcium nitrate was substituted for magnesium nitrate by 
increments of a hundredth of the total salt concentration of the 
solution. In the former case, however, the salt concentration was 
DISTILLED WATER — 
Fic. 16.—Seedlings of culture 14, experiment 8. 
such that magnesium nitrate alone killed the roots, whereas in the 
latter case it was such that magnesium nitrate alone retarded the 
erowth of lateral roots and did not kill the primary. In experiment 
C the lateral roots did not attam as perfect a development as in dis- 
2 
tilled water until the ratio of magnesium to calcium reached = In 
experiment 5, on the other hand, the first increment of calcium 
(making the ratio of magnesium to calcium =) permitted laterals to 
develop as well as in distilled water. The concentration of calcium 
231 
Fee ee Sen 
