1 889.] BOTANICAL GAZETTE, 205 



and some would appear to belong to the former which are not so accred- 

 ited. 



Physiology of tannin. 3 



Concerning no substance found in such quantity in plants has our 

 knowledge remained so long so defective as in regard to tannin. This is 

 largely due presumably to the rare combination of botanical knowlege 

 with the skill of the analytical chemist. Most botanists who have studied 

 it have used microchemical methods, and most chemists who have given 

 it any attention have paid little heed to its functions or origin in the 

 plant. The unsatisfactory state of our knowledge can be discovered by 

 consulting any, even the most recent, of our text-books. After consider- 

 able study with microchemical methods, Dr. Kraus, of Halle, undertook 

 a thorough comparative study of the origin and behavior of tannin, using 

 the most approved methods of the quantitative chemist for determining 

 its presence and amount. These were chiefly the Schr<>der-L6wenthal 

 method of titration with chamseleon, and Fleck's method of precipitation 

 with neutral cupric acetate, ignition, and weighing as CuO. The former 

 method, while not indicating the total amount present, is nevertheless 

 suitable for comparative studies. Kraus's chief conclusions are as fol- 

 lows : 



Tannin is formed in green leaves under conditions which coincide 

 closely, though not exactly, with those of assimilation. Tannin is not, 

 however, a product of assimilation of carbon, for this process can and 

 does go on independently. Tannin once formed does not undergo chem- 

 ical alterations, but is carried out of the leaves along the veins and petiole 

 to places of storage. In woody twigs it descends chiefly or only in the 

 bark. This descent begins with the unfolding of the leaves and con- 

 tinues late in the growing season. The tannin of germinating rhizomes 

 even though a large portion of their weight (25-40 per cent.) disappears 

 to form the new organs, does not diminish in quantity. On the contrary, 

 it may increase. All the new organs contain tannin, which must there- 

 fore be formed in the darkness. Neither in woody plants nor in seeds 



does tannin behave as a reserve stuff. 



After discussing the two modes of formation of tannin indicated 

 above, the author gives an account of its anatomical relations, treating 

 (a) of the transitory tannin, the green tissues in which it is formed, the 

 conducting and storage tissues, and (b) of the autochthonous or resting 

 tannin in growing-points, tannin-sacs, etc. The tannin of galls he calls, 

 provisionally, autochthonous. Chapters on the methods of research and 

 a sketch of previous investigations are followed by the details of his ex- 

 periments, covering 52 pages. 



It strikes us that the author is rather inclined to depreciate or ignore 

 thp 1oKa M ~f •*»*«;«*,« u«>iuitiiMtfiML and that his assumption that he 



•Kra i, GKEGOR.-Grimdlinieii zur Physiologic des Gerbstoffs. pp. vi. 131- 8°. Leip- 

 zig: W. Engelmann. 1889. M. 3. 



