THE POTATO TUBER. 
79 
advances. The horizon of research is becoming still further 
widened by the accession of that branch of knowledge of 
comparatively modern origin which results from the fusion 
of Biology and Chemistry, namely, Biological Chemistry, 
without which the elucidation of the life activities of plant 
organisms cannot be regarded as other than incomplete. 
Summary. 
The general conclusions to be derived from the ex- 
perimental results here presented may be briefly enumerated 
as follows :■ — 
1. The skin of the cultivated tuber is a structural 
covering, the walls of its component cells being of a corky 
nature. Its structure and the disposition of its layers in- 
dicate its protective function. 
2. The results of physiological and biochemical in- 
vestigation show that it is eminently protective against ex- 
cessive losses of moisture and stored nutrient substances 
of the tuber. 
3. The skin of the mature undamaged tuber is imper- 
meable (under ordinary circumstances) to various salts and 
acids in solution. This impermeability is not possessed by 
blight-infected tubers. 
4. Biologically the skin of the tuber is of considerable 
importance in offering a barrier to fungous and bacterial 
invasion. 
