TRUE & HARVEY: ABSORPTION OF CALCIUM SALTS 505 
by the distilled water, and seems to represent a fairly well-defined 
irreducible minimum. This point is marked by a lower ion content 
than the similar minimum seen in the distilled water. It seems clear 
that the substances giving to distilled water its conductivity are not 
absorbed to as dilute a minimum concentration as is calcium nitrate. 
It will be noted that only in the two more concentrated members 
of the series are there any absorbable electrolytes remaining at the 
end of the experiment, and therefore only in these cultures is the total 
capacity of these plants to absorb this salt measured. In these cases 
the total absorbed salt equals 565 and 713 grm. norm. X 107° re- 
spectively. 
An inspection of the graphs shows that in nearly all solutions of 
the salt there occurs a time at which the plants reduce the conductivity 
of the solution to a minimal concentration, a point that may be 
assumed for present purposes to represent that of maximum absorption. 
In some cases experiments have been closed before this point has been 
reached in a number of members of the series (usually the more con- 
centrated ones), owing to the well-marked exhaustion of the plants 
in a number of the cultures. In such a case the absorption maximum 
may not have been reached, although probably in most cases it has 
been approached. 
It is interesting to compare the original concentration of the differ- 
ent solutions with the corresponding concentration at the time of 
maximum absorption. By this means one is able to ascertain how 
much of the salt is absorbed or how much net loss the plants have 
suffered calculated at the time of greatest absorptive efficiency. 
Carrying out the calculation referred to for the cultures included in 
this experiment the results seen in the following table (1) are obtained. 
A glance shows that about 37.0 grm. norm. Ca(NQOs3). are required 
by five squash seedlings growing in 500 cc. of solution to enable them 
to protect such ions as are mobilized from their reserves against the 
leaching action of the distilled water. This stated in terms of the 
quantity of Ca( NOs). per plant would be about 0.00028 grm. absorbed 
during a period of about two weeks. 
As the salt content is increased, absorption increases in approxi- 
mately the same magnitude leaving an unabsorbable residue of 
approximately 34 grm. norm. X 10-® Ca(NOs3)o. This minimum is 
here calculated as Ca(NO3)2, but it should be clearly understood that 
the substances actually composing this residue may be, and probably 
in considerable part are, of quite other composition. Indeed, the 
substances indicated as Ca(NOs)2 at all stages of the experiment, 
especially the later ones, doubtless consist in part of other materials, 
largely coming by exosmosis from the interior of the test plants. The 
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