654 SUMMARY OF CURRENT RESEARCHES RELATING TO 



that the substance previously described by him as chlorophyll -green is 

 in reality a compound of that substance with sodium. He has now 

 succeeded in separating pure chlorophyll-green by the following process. 



Grass-leaves are boiled in water from a quarter to half an hour, then 

 washed in water, pressed, and dried in the dark. The chlorophyll- 

 pigment is then extracted with boiling alcohol, and the solution saponified 

 by heating for three hours with a slight excess of caustic sodium. The 

 excess of sodium is converted into carbonate by carbonic acid, and the 

 mixture thus obtained dried in a water-bath. The chlorophyll-yellow 

 is then extracted by ether, in which the compound of chlorophyll-green 

 with sodium is quite insoluble, and afterwards by a mixture of equal 

 parts of alcohol and ether, in which it is only slightly soluble, and the 

 residue again by a mixture of equal parts of alcohol and ether and 

 phosphoric acid. This sets free the chlnrophyll, which dissolves in the 

 mixture of alcohol and ether, and can be evaporated as a shining black- 

 green perfectly solid brittle substance, insoluble in water, benzol, and 

 bisulphide of carbon, soluble with difficulty in pure ether, easily in 

 alcohol. The solution has a beautiful pure green colour, which becomes 

 red and strongly fluorescent when concentrated. It offers great resis- 

 tance to reagents, especially mineral acids. Its exact composition has 

 not been ascertained, but it contains iron and nitrogen. 



The author then describes the process for obtaining pure chlorophyll- 

 yellow, which crystallizes in orange-red crystals, ins duble in water, but 

 soluble in alcohol, ether, chloroform, and benzol with a dark yellow, in 

 bisulphide of carbon with a red colour. The yellow chlorophyll of 

 flowers and fruits, and that contained in the jietals of the poppy, is 

 identical with the clilorophyll-yellow of leaves. 



The optical j)roperties of the various chlorophyll-pigments are then 

 described ; and finally, the mode in which these pigments are contained 

 in living chloroplasts. The author states that the green substance which 

 fills up the vacuoles of the chlorophyll-graius is not a solution, but 

 consists of combinations of the two chlorophyll-pigments with fatty 

 acids, which possess a half-solid consistence ; and the same is true of 

 the chromoplasts. 



Physiology of Tannin.* — Herr G. Kraus gives a resume of the most 

 trustworthy investigations that have yet been made of the nature and 

 function of tannin ; the mode of investigation being Loewenthal- 

 Schroeder's, viz. trituration with chameeleon, and extraction with water 

 until the water becomes perfectly colourless. 



Tannin is produced in the leaves under the influence of light ; its 

 decrease when the light is removed, is due, not to its decomposition, but 

 to its transference to the stem and branches, and a fresh formation of 

 secondary tannin, as it is termed by the author, takes place in the newly- 

 formed organs, even in the dark. The conditions for the production of 

 tannin are, in general, the same as those for carbonic assimilation, and 

 the formation of this secondary tannin is closely analogous to the similar 

 phenomenon in the case of starch. 



The author regards tannin, from a physiological point of view, simply 

 as an excrementitious product, and also, in some cases, as serving to 

 protect the plant from being devoured by animals, or from decay. 



* 'Grunrllinien zu einer Physiologie rl. GerbstofiFs,' 8vo, Leipzig, 1889, 131 pp. 

 See Bot. Centralbl., xxxviii. (1889) p. 447. 



