274 SUMMARY OP CURRENT RESEARCHES RELATING TO 



frequently be seen borne to the surface of pools of stagnant water by 

 innumerable minute bubbles of oxygen gas. Some of the simplest of 

 the unicellular algse, e. g. Protococcus pluvialis and P. palustris, exhibit 

 this peculiarity to a remarkable degree. T. L. Phipson has cultivated 

 some of the last-mentioned plants by exposing pump-water to air and 

 light for some weeks, and as soon as good growth was obtained, small 

 dead branches of poplar were put in the water; the Protococcus 

 developed rapidly upon them. The branches can then be put in 

 flasks full of water, and the production of oxygen observed ; this takes 

 place immediately the flasks are exposed to the sun's rays ; the oxygen 

 comes off in the minutest bubbles, but in such great numbers as to 

 form a froth on the surface ; in some higher plants, e. g. Achillea 

 Millefolium, the gas collects at the end of the leaves, and comes to the 

 surface in large bubbles. If the flask is inverted the evolution of gas 

 continues for about three days ; the introduction of a minute quantity 

 of caustic soda stops it on the first day by depriving the plant of 

 carbonic anhydride. On renewing the water after three days, the 

 evolution recommences, and so by keeping up a constant supply of 

 pump-water and the production of oxygen, may be kept up to all 

 appearance indefinitely. 



The author has devised a simple apparatus for this purpose. 

 A wide-mouthed bottle with tubulure near the bottom, is fitted with a 

 gas delivery tube, and a tube with tap connected with a water-supply ; 

 the water must neither be boiled nor distilled, nor must it be in the 

 slightest degree alkaline. A tap is put in the tubulure and is used 

 to empty the bottle. Some of the poplar branches are placed in 

 the bottle, water is run in, and the bottle exposed to sunlight ; the 

 oxygen can be collected in a gas-holder. After three days the old 

 water is run out of the bottle and fresh water run in. The author 

 suggests that by employing graduated vessels, &c., the apparatus might 

 be used as an actinometer. The gas produced contains about 98 per 

 cent, oxygen. The author remarks incidentally that carbonic anhydride 

 in presence of sunlight is not decomposed by plants, but simply 

 absorbed, water and hydrogen dioxide being equally essential for the 

 production of oxygen, and the gas being evolved from the tissue as a 

 consequence of the absorption. 



Chromatophores of Marine Diatoms.* — O. Miiller describes the 

 peculiar form and structure of the chromatophores in some marine 

 diatoms, hardened and coloured according to Pfitzer's nigrosin-picric- 

 acid method. 



In Pleurosigma angulatum the chromatophores consist of two 

 very long bands, twice the length of the longitudinal diameter of the 

 cell or more, comparatively narrow, much lobed and indented, but 

 never perforated. They are arranged symmetrically on each side of 

 the cell. For their whole length their surface is applied to the cell- 

 wall, and separated from it by only a thin layer of protoplasm. A 

 midcile portion of each band, about one-third of its entire length, runs 

 undivided to the inner surface of the upper shell — i. e. the shell which 



* Ber. Dcntsch. Cot. Gesell., i. (1883) pp. 478-84. 



