510 BROOKLYN BOTANIC GARDEN MEMOIRS 
they are able to do so. This required minimum quantity is probably 
of considerable physiological significance. At higher initial con- 
centrations, from 53.5 to 384.0 grm. norm. loss of ions during the 
early days of the experiment becomes less marked as the concentration 
increases. Absorption usually begins more promptly and proceeds with 
greater speed as the quantity of ions present increases until in all cases 
but one the concentration of ions remaining in the solution is reduced 
__[SauAsH CaCl, 18°C. 
700 700 
650 
550 50 
De) 
Ss 00 
450 
S 
~ 400 
Ss 
3 0 
S 
= 300 
& 50 
S 
= 
lf 200 
1/50 
PERE 
Bae ae 
aes Bee, 
CO OE ZA Se aaa) 
Fic. 3. For explanation see text. 
to the unabsorbable minimum at an average concentration of approxi- 
mately 27 grm. norm. X 107®. Only when the original concentration 
of 582.4 grm. norm. X 107° is reached do we find the quantity of ions 
offered greater than can be reduced by the seedlings to the unab- 
sorbable minimum. These relations are seen in the numerical data 
given in Table 3, in which thé concentration relations are shown as 
they exist at the time of maximum absorption. Here again the 
similarity to the situation seen in solutions of Ca(NQOs)z is striking. 
If we are justified in concluding that the depressing action of the 
SO, anion is responsible for the great reduction of root absorption 
