METABOLIC PROCESSES IN THE PLANT. 337 



lings of Vicia grown in the dark, they prove to be very rich in 

 tannins. 



If it is desired to study the formation and subsequent be- 

 haviour of tannins microchemically, it is best to proceed as 

 follows : We inject the objects under the air-pump with a 10 

 per cent, solution of Potassium bichromate, let them die in it, 

 and then, after careful washing, examine them, either at once or 

 after preserving in alcohol. By this means we readily determine, 4 

 e.g., that in seedlings of Vicia Faba grown in darkness, secondary 

 tannin appears in specially large quantities in the epidermis and 

 sub-epidermal tissue, and in the parenchyma surrounding the 

 vascular bundles. The main root of the seedling contains much 

 tannin in the cortex ; its central cylinder is almost devoid of 

 tannin. 



Secondary tannin is also contained in the stems of seedlings of 

 Phaseolus multiflorus, grown in the dark. It occurs in special 

 tubes in the sieve region of the vascular bundles. The radicle of 

 Phaseolus does not contain tannin ; the embryo also of dormant 

 Phaseolus seeds contains no tannin at all. To detect the tannin 

 we employ in this case likewise a solution of Potassium bichrom- 

 ate or of Ferric chloride. 



We cut oft' in spring twigs of Lonicera tatarica, and put them 

 with their base in water. The buds of some of the twigs are 

 allowed to unfold in the dark, those of others in the light. 

 Primary tannin can only be detected by microchemical means 

 in the axis of the young shoots which have developed in the light 

 (e.g. in the epidermis and cortical parenchyma). 'The shoots 

 produced in the dark are devoid of tannins. For further infor- 

 mation, see Biisgen's treatise. 



1 See Sanio, Botan. Zeitimg, 1863, p. 17. 



- If the material with which we are dealing is not too hard, we may use one 

 of the so-called Excelsior mills, to be obtained at a price of 30-40 mks. from 

 Gruson in Magdeburg-Buckau. For grinding woods, etc., suitable mills are 

 to be obtained of G. Wenderoth in Cassel. 



3 For further particulars see Kraus, Grundlinien zu einer Physiologic des 

 Gerbstotfs, Leipzig, -1889, and Berichte iiber die Verliandlungen der Commission 

 znr Fcstatelliing einer cinheitlichen Methodc dcr Gcrbstoffsbestimmung, Fischer, 

 Cassel, 1885. 



4 See Biisgen, Beobachtungen iiber das Vcrhalten des Gerbstoffes in den 

 Pjlanzen, Jena, 1889. 



P.P. 



