20 ABSORPTION AND EXCRETION OF SALTS BY ROOTS. 
same, although the gram-molecular concentration would have be- 
come twice as great and the osmotic pressure higher by one-third. 
In carrying out an experiment the conductivity of each solution 
was determined before use. The conductivities obtained at the end 
of the experiment were translated into terms of concentration of the 
original salt by interpolation and extrapolation into the original 
conductivity series; thus the error due to carbonic acid and unknown 
electrolytic Impurities of the distilled water was eliminated as far as 
possible. 
EXPERIMENT 1. 
| | eae 2M 
Experiment 1 embraced solutions grading by increments of 500,000 
26 M 
500,000 Mg (NO,),; duration of cultures, 9 
days; temperature of solutions 19.5° at beginning of experiment, 21° 
at end. 
from distilled water to 
TaBLE I.—Statement of results, experiment 1. 
INumiberon i culitwre renee terre eases 1 2 3 4 5 6 7 
Concentration: 
Beforerenowthienes eee ese ees 0 2M 4M 6M 8M 10 M 12M 
500, 000 | 500,000 | 500,000 | 500,000 | 500,000 | 500,000 
Miter prowithe eens eee hele eee 22 M 13M 20 M 14M 20 M 14M 11M 
500, 000 | 500,000 | 500,000 | 500,000 |} 500,090 | 500,000 | 500, 000 
INUmibeHofculiine= == se4- seers eee eee 8 9 10 11 12 13 14 
ation: 
ae a: es . 14M | 16M | 18M | 20M | 22M | 24M | 26M 
BONS GUOWMIDS aq saacpecotcoacessc: 500, 000 | 500,000 | 500,000 | 500,000 | 500,000 | 500,000 | 500,000 
: ‘ sm | 2M | 1M | 14M | 1M | 19M | 22M 
AMINES EPROM Mtl soagocac2es28scusses 5: 500,000 | 500,000 | 500,000 | 500,000 | 500,000 | 500,000} 500, 000 
These results show that pea roots excrete more electrolytes than 
they absorb when grown in solutions of magnesium nitrate weaker 
12 
2M 
than 500,000° and, conversely, that they absorb more than they 
12 M 
excrete when grown in solutions more concentrated than 500,000" 
This showing is made more evident to the eye by plotting the results. 
(Fig. 9.) The point at which the curve of change in concentration 
intersects the horizontal axis indicates the concentration (about 
12M 
500,000 
electrolytes at approximately the same rate. 
231 
) of magnesium nitrate at which the roots excrete and absorb 
