72 
F. STOWARD D.SC. : 
We may in an indirect way strengthen this conclusion 
by removing the skin and steeping the peeled tuber, thus 
prepared, in brines. In the following experiments, typical 
of several similar essays, are given the results of determina- 
tions of the change in the strengths of the brines used at 
intervals during the progress of these experiments. 
Table VI. 
Grams of chlorides expressed as NaCl per ioo cc of 
solution. 
At commencement of experiment . . 4.27 9.32 17.91 
After 5 days’ steeping 3.77 6.58 11.93 
„ 6 „ „ — 6.58 11.84 
It will be noted that as the result of the removal of the 
skin of the tuber, common salt rapidly and freely diffuses 
into the peeled tuber. This process of diffusion as the 
above analytical data show, proceeds rapidly at first, but 
from the fifth day and probably earlier the rate of diffusion 
slows down until about the sixth day a state of balance is 
attained and a point is reached at which the rates of entry 
and egress of salt into and from the steeped oojects are 
practically equal. 
As in the preceding series, the absorption of salt by 
peeled tubers may be directly investigated and a more 
accurate measure made of the actual salt absorptive capacity 
by estimation of the amounts of chlorides in the material 
itself. Below are given the data afforded by such a series 
of determinations 
Table. 
Percentage of chlorides calculated on air-dried tissue. 
Chlorides Approximate 
(Calculated relative salt 
as NaCl) content. 
Peeled tubers (untreated) 0.28% 1 
Peeled tubers rfter 6 days’ steep- 
ing in 10% brine 2.29 10 
Peeled tubers after 6 days’ steep- 
ing in 20% brine 4.96 20 
Comparison of these experiments (peeled tubers and 
the foregoing (intact tubers) evidently shows that the skin 
presents a barrier which greatly retards the entry of common 
salt into the tissue of the tuber. This impermeability of 
the tuber to salts in solution is undoubtedly an important 
biological factor. Important as the skin may be as a 
barrier to bacterial and fungoid invasion, it is equally 
essential that the reserve substance of seed tubers when 
planted in the soil should have ample protection. Free 
