726 SUMMARY OF CURRENT RESEARCHES RELATING TO 



placod for an hour in a mixture of 1 vol. aqueous solution of ferrid- 

 cyanide of potasli (1-10) and 2 vols, acetic acid (1 vol. acid sp. gr. 

 1-063 to 1 vol. water). He then decanted with 60 per cent, alcohol 

 until the fluid no longer had an acid reaction, and no longer hecame 

 blue on the addition of ferridchloride, and finally placed the prepara- 

 tions in a solution of ferridchloride. By this means the nuclei, 

 starch, and to some degree the chlorophyll-granules (from which the 

 colour had been removed by absolute alcohol) were stained blue, the 

 rest of the protoplasm remaining unstained. 



As specially suitable for this method, strips of epidermis from the 

 leaves of Orchis are recommended. With Spirogyra this procedure 

 does not yield tho desired results, although the cell-contents of this 

 alga are rich in albuminoids. The absence of the reaction depends 

 possibly upon some specific arrangement of the albumen molecules ; 

 consequently, Spirogyra has to be treated by the biuret test, which is 

 done as follows : — The alga? are steeped for 12 hours in a dilute solu- 

 tion of potash and yellow prussiate of potash, and next in a solution 

 of the same salt with acetic acid. After being washed with water, 

 and then in 60 per cent, alcohol, they are finally placed in a dilute 

 solution of iron chloride. Or, instead of the foregoing, the algse may 

 be placed for 15 minutes in a 25 per cent, solution of potash, and then 

 for an hour in an acid solution of prussiate of potash. Having been 

 washed as before, the chlorophyll is withdrawn with absolute alcohol, 

 and the blueing of the protoplasm effected with ferridchloride solution. 



With regard to the biuret test, which consists in the application 

 of copper sulphate and of potash, the author remarks that a rose- 

 colour is imparted to the protoplasm of the older cells if the order of 

 the reagents be reversed. 



Micro-chemical Reaction for Demonstrating Reducing Sugars.* 

 — Herr A. Meyer recommends the following procedure : — 



Sections, two to four cell-layers thick, of the plants to be ex- 

 amined are placed for a short time in a saturated watery solution of 

 sulphate of copper, then shaken quickly once in water and directly 

 after immersed in a boiling solution of 10 grms. Seignette salt and 

 10 grms. caustic potash in 10 grms. water. After some seconds, in 

 all the cells which contain reducing sugar, a precipitate of copper 

 oxydul is thrown down while all the other cells remain perfectly 

 colourless. By this method the disturbing formation of copper oxide 

 is prevented, and a more accurate conclusion as to the distribution of 

 sugar in the tissues is possible. 



Polarization of Bi-axial Crystal Plates cut vertically to an 

 Optic Axis.j — Flat, optically bi-axial crystals, which are cut vertically 

 to one of the optic axes, must, according to theory, always remain 

 uniformly dark when examined under the Microscope with crossed 

 nicols with one complete turn of the stage. Herr E. Kalkowsky 

 shows that the appearances required by theory are never attained in 



* Ber. Deutsch. Bot. Gesell., iii. (1885) p. 332. 



t Zeitbclir. f, Krystallog. u. Mineral, ix. (1884) pp. 486-97 (1 pi.). 



