THE POTATO TUBER. 
63 
The chief object of this paper, as its title is intended 
to imply, is a consideration of the physical properties and 
physiological attributes of the skin of the potato tuber. 
Morphological and histological observations, coupled 
with micro chemical tests, furnish information which is of 
a suggestive character only as to tire possible role of the 
skin in the general economy of the tuber. The minute 
anatomy of the skin, the disposition of its layers, its cellular 
structure, and the demonstration of the corky character 
of the walls of these cells, all belong to the domain of de- 
scriptive data. Such data are admittedly essential and 
useful, but possess chiefly a suggestive or speculative value, 
in so far as concerns the functional attributes of the skin, 
on evidence of this kind we may conceive in a rough qualita- 
tive fashion that the skin of the tuber is a protective covering, 
and we may consider that the observations cited are entirely 
in accord with this view. In other words, histological in- 
vestigation, as we have seen, is distinctly illuminative in 
regard to the structural features of the skin, but it is in- 
adequate as a means of affording any very definite informa- 
tion as to the nature of the suggested protective function 
of the skin of the tuber. Experimental enquiry into the 
physiological attributes of a vegetable organ or tissue is 
often confronted on its very threshold by this difficulty ; 
it frequently involves mutilation of the object which we 
propose to investigate. It is not, therefore, always 
possible to differentiate in how far the results which follow 
on mutilation are strictly physiological or pathological in 
character. 
We will first consider experiments designed to ascertain 
xhe results, expressed in terms of the comparative loss of 
weight, attendant on : — 
(1) Complete removal of the skin and eyes (peeled 
tubers) . 
(2) Bi-section of the tubers (cut sets) ; 
and compare these results with those yielded by unmutilated 
but otherwise similar tubers. The selected conditions of 
experiment being similar for the three series, i.e., the tubers 
being exposed to the same temperature and other external 
conditions. In each instance the loss of weight is calculated 
as a percentage on the initial weight of the material ex- 
amined. 
The data contained in the table beneath represent 
only a selection form several series of similarly performed 
experiments. 
