GENERAL CHARACTERS. 
19 
October, thus pointing to the possibility of its being 
a storage material to assist the plant in blooming and 
perfecting its seed. 
The questions which naturally arise from a consid¬ 
eration of the various facts are, Do the tannins result 
from the decomposition of starch? Are they closely 
related to the resins? Are they a reserve material, or 
simply a useless by-product? These problems remain 
to be worked out, and the answers may be found to 
vary with the kind of tannin. For instance, gallotan- 
nic acid is simply a morbid deposition of the compound 
resulting from the sting of an insect, while the other 
tannins vary according to the circumstances under 
which they have been formed. 
Probably the most recent contribution to this subject, 
and one established on many experiments, is the mono¬ 
graph of Kraus, who has established some facts con¬ 
cerning the formation of tannin, but has not offered a 
solution of the various problems. He considered the 
tannins of different origin to be physiologically alike. 
This was stated soon after by Reinitzer to be incorrect. 
Kraus further found that light and carbon dioxide are 
essential agents of the formation of tannin in leaves. 
Leaves which are not green are not capable of producing 
tannin. The outer leaves of a plant, exposed to direct 
sunlight, contain more tannin than the inner leaves. It 
is not a product of the assimilation of chlorophyll grains; 
the oak, willow, and alder assimilate in dull weather 
without increasing in tannin. The tannin produced 
in the leaves passes into the branches and roots, and 
there is no experimental evidence that the tannin which 
has once passed into the rhizome undergoes further 
