THE POTATO TUBER. 
73 
and unrestricted diffusion, for example, of soluble salts in 
the soil into the tissue of the tuber might be disastrous, 
especially during the period prior to the establishment of 
the young plant when it relies entirely for its nutrition on 
the reserve storage materials in the planted tuber. When 
this period is passed and the young plantlet has developed 
its root system it regulates within certain limits its intake 
of soluble inorganic food materials from the soil. 
Similarly established experiments with less mature 
intact tubers which were separately steeped in solutions of 
the following compounds : nitrate of soda, nitrate of potash, 
sulphate of ammonia, of 10%, or in sulphate of iron of i% 
strength, tor variable periods of xo. 15 or 24 hours’ duration, 
yielded results which parallel those afforded by similar 
material steeped in common salt solution. That is to sav, 
in no single instance was there definite evidence pointing to 
the absorption by the tuber of any of these salts in quantity. 
Certain tests carried out with these tubers at first seemed 
to suggest that these salts stimulate sprouting. This was 
notably the case with those which had been steeped in 
sulphate of ammonia. Control tests, however, performed 
by steeping tubers in water alone, rather tend to discount 
this appai ent result and render it equivocal. The question 
of this stimulative effect exercised by this treatment awaits 
further trial. The ground so far covered regarding the 
behaviour of the tuber when steeped in solutions of common 
salt and also the other salts enumerated indicates that the 
skin is practically impermeable to these compounds, but the 
evidence so far adduced cannot be said to show other than 
inferentially whether the comparatively small amounts of 
these various salts which are absorbed penetrate the tissue 
of the tuber solely by way of the skin or buds. 
Experiments with acids and especially with sulphuric 
acid throw light on this question, and we may now turn 
with advantage to this portion of the enquiry. 
The Steeping of Tubers in Solutions of Acids. 
The Impermeability of the Skin to 
Sulphuric Acid. 
(a) Blight-free mature tubers. 
When well-ripened mature tubers with undamaged skins 
are steeped in solutions of sulphuric acid of 2.5, 5 or 10% 
strength for periods of time ranging from 1 to 20 hours, 
or even longer, the amounts of acid which are absorbed 
are relatively small, not amounting to more than about 
0.09% of acid calculated on the total weight of the steeped 
material. A few concrete examples will render this state- 
