138 PLANT ANATOMY. 
above indicated, sharp chemical distinctions exist, which are ren- 
dered evident, especially, upon dry distillation. When subjected 
to this treatment, the tannic matters which produce a blue color 
with ferric salts afford pyrogallol (pyrogallic acid), while those 
producing a green color with ferric salts, on the contrary, afford 
pyrocatechin. If the tannic matters are melted with caustic: 
potassa, those giving a blue color with iron salts afford pyro- 
gallol, as in the former case; the other tannic matters, on the 
other hand, produce protocatechuic acid. 
The knowledge of the different members of the chemical 
family of tannic matters, in their details, is still very fragment- 
ary. A method is also still wanting which meets all demands 
for the quantitative estimation of tannic acids in all-the numer- 
ous Cases where they cannot be extracted with a tolerable degree 
of purity by ether-alcohol, as, for example, from nutgalls. Be- 
sides, if it be considered that the amount of tannic matter is 
subject to the fluctuations of vegetation, it cannot be greatly 
wondered at that the analytical statements relating to it deviate 
widely from each other. Many such estimations have been 
made from a technical standpoint, as in the case of oak-bark, 
so that the literature on this subject is quite extensive.’ The 
oak-bark appears to be capable of containing a maximum of 
twenty per cent of tannic matter, or more than any other part. 
of a plant which concerns us here,’ unless we take into consider- 
ation the galls (see the chapter at the end of this work: Patho- 
logical Formations). The latter, namely, are to be regarded 
simply asa morbid accumulation of tannic acid. The gallo- 
' It may suffice to mention here the following: ‘‘ Bericht iiber die Ver- 
handlungen der Commission zur Festellung einer einheitlichen Methode 
der Gerbstoffbestimmung, gefiihrt am 10. November 1883 zu Berlin. 
Redaction und Einleitung iiber die bisherigen Verfahren der quant. Be- 
stimmung des Gerbstoffs von C. Councler. Nebst Untersuchung tiber 
die Léwenthal’sche Methode von J. V. Schroeder,” large 8vo (IV., pp. 
79), Cassel, Fischer, 1885. 
* The bark of the Australian Eucalyptus corymbosa is stated to con- 
tain twenty-seven per cent of tannic acid (Jahresbericht der Chemie, 
1868, 807), the Myrobalans forty-five per cent: Dividivi, the pods of 
Cesalpinia coriaria Willd., fifty-five per cent, 
