832 SUMMABY OF CURRENT RESEARCHES RELATING TO 



Reagents for Tannins in Vegetable Cells.* — W. Gardiner speci- 

 fies objections to all the micro-chemical reagents for tannins hitherto 

 used. Iron sulphate he finds convenient when the products are blue 

 and not green. He prefers to use a solution of ammonium molyb- 

 date in concentrated ammonium chloride ; this gives with tannins a 

 copious yellow precipitate. It cau also be used for determining the 

 presence of gallic acid, with which it produces only a red colour ; 

 the compound with gallic acid is soluble in ammonium chloride, 

 while that with tannin is not. 



The determination of tannins in tissues preserved in alcohol is 

 facilitated by the fact that dead protoplasm gives a permanent pre- 

 cipitate with tannins. 



The author regards the tannins as secondary products of meta- 

 stasis, especially when this process is very active, and thinks that 

 they have no further use. In the old leaves of a cutting of the 

 cherry-laurel which had already put out roots and shoots, the quantity 

 of tannin had considerably increased. 



Microscopical Examination of Chestnut-meal.t — T. F. Hanausek 

 gives the following microscopical characteristics of the various parts 

 of the sweet chestnut. The testa of the chestnut consists of three 

 layers. The cells of the outermost layer are polyhedral thick-walled 

 plates with yellow or dark-brown angular flakes (tannin?). Many 

 bear stiff cylindrical unicellular hairs, varying in thickness from • 018 

 to • 029 mm., and of variable length. Some have thin and others very 

 thick walls ; the former contain tannin. The middle layer is composed 

 of tangentially elongated, thin-walled, bright-red parenchymatous 

 cells, which swell up in potash to a broad elliptic form, and are 

 coloured of a beautiful violet-blue by chloride of iron. It has also 

 strong vascular bundles and large cavities. The innermost fibrous 

 layer forms a narrow light-brown streak composed of thin-walled 

 fibrous elements. 



The two cotyledons consist of an amylaceous parenchyma. The 

 outermost layer of cells are narrow five- or six-sided radially arranged 

 prisms, with a diameter of 0* 007-0 •01 mm.; in the radial direction 

 they are three or four times as long. The very small colourless protein- 

 grains are only coloured pale yellow by iodine, on account of the 

 envelope of oil which surrounds them. The amylaceous cells have a 

 diameter from • 055-0 ' 075 mm., and contain, besides starch, a parietal 

 layer of albuminoids and oil. The starch-grains are sometimes simple, 

 sometimes double. The simple grains are extremely variable in form ; 

 the most characteristic forms are triangular, and one has an acute 

 projecting appendage. Some resemble the cap-shaped partial grains 

 of tapioca. The nucleus is central and difficult to detect ; stratifica- 

 tion is indicated in the largest by two or three inconspicuous lines. 

 The polarization-cross is very conspicuous. The smaller spherical or 

 ellipsoidal grains have a diameter of from 0*005-0 "009 mm.; the 



* Proo. Oamb. Phil. Soc, iv. (1883) pp. 387-94, 



t Zeitschr. f. Landwh-tschaft. Gewerbe, 1883, pp. 3-5 (3 pis.). See Bot. 

 Ceutralbl., xiv. (1883) p. 180. 



