346 



KNOWLEDGE. 



September, 1913. 



Further details of Brown's important work, and of various 

 other recent researches on the interesting aquatic flora of 

 ponds and streams, are given in the review mentioned above, 

 which extends to nine pages and deals with every important 

 publication on the aquatic and marsh flora during the last 

 two years, with references to earlier work in addition. 



CUSHION PLANTS.— Another interesting article in the 

 Journal of Ecology for June deals with the structure, 

 physiology, and ecology of cushion-plants, based on an 

 important work by Hauri (Beih. Bot. Centralbl., Band 28), 

 of which the following is a brief summary. Cushion plants 

 are perennial, usually evergreen, more or less stunted plants 

 of compact and usually rounded growth and dense branching, 

 the branches being closely covered with relatively small stiff 

 sessile leaves which are either appressed or are packed 

 together with hairs. Hence the plant forms a living spongy 

 cushion characterised by firmness, compactness, and closed 

 growth, which reacts as a whole to the factors of the environ- 

 ment. Details are given of the main features of these 

 remarkable plants, under such headings as general form, 

 branching, root system, firmness and closure, and packing 

 material, and cushion-plants are divided into six classes 

 (illustrated by a full-page set of illustrations) of which 

 examples are given. In the general sketch of the biology and 

 ecology of cushion-plants the following points are noted, 

 (a) The capacity for absorbing and retaining large quantities 

 of water, serving to regulate the temperature of the plant 

 during alternate warming and cooling of the air, to keep the 

 air in and around the plant relatively moist, to make the 

 underlying soil moist and warm, and in some cases to supply 

 water directly to the aerial organs by means of adventitious 

 roots. (b) The crowding and overlapping of the leaves, 

 serving as a protection against direct insolation, and producing 

 wind-still and moist capillary interspaces between the 

 branches, thus minimising loss by transpiration, (c) The 

 compact growth of the branches in the cushion, which 

 enhances the capillary arrangement due to (6) and serves to 

 collect sand and other wind-borne debris as well as the dead 

 leaves of the plant itself, besides being the main factor in pro- 

 ducing the cushion habit itself with its obvious protective 

 advantages, (d) The packing material, which enormously 

 enhances the water-holding capacity of the cushion, provides 

 food in the form of humus, and enhances the rigidity and 

 hardness of the cushion. The degree of hardness attained in 

 some cases may be judged from the fact that in some Andine 

 species, such as Azorella tnadreporica, the plant turns off 

 a revolver shot at point-blank distance, and specimens can 

 only be obtained by breaking up the cushion with a hammer ! 



CHEMISTRY. 



By C. Ainsworth Mitchell, B.A. (Oxon), F.I.C. 



WILD LETTUCE RUBBER.— Mr. C. R. Fox, writing in 

 the Journ. Ind. Eng. Chem. (1913, V, 477), gives an 

 account of two species of wild lettuce which grow in the 

 United States, and suggests the possibility of utilising them 

 for the production of rubber. One of these, Lactuca 

 canadensis, which is popularly known as " trumpet weed," 

 yields when bruised a thick milky juice, or latex, containing 

 over two per cent, of rubber. It also contains upwards of 

 13 per cent, of a brittle brown resin, which dissolves readily 

 in alcohol and acetic acid, and a slightly acid substance with 

 an intensely bitter taste. More than forty years ago it was 

 stated by Maisch that the juice of this lettuce contained a 

 bitter principle, " lettuce opium," and Mr. Fox suggests that 

 extraction of this drug combined with the separation of the 

 rubber might be found a profitable industry. Owing to the 

 presence of the acid bitter principle the rubber would require 

 washing with alcoholic alkali. 



The other species of lettuce, L. scariola, is an annual 

 plant, the juice of which contains less rubber (1-58 per cent.) 

 and a smaller proportion of resin. The rubber derived from 

 either of these plants is stated to possess excellent physical 

 properties. 



ACTION OF CAUSTIC LIME ON SOIL. — It is 



common knowledge that soil is materially improved by 

 suitable additions of caustic lime, and this is usually 

 attributed to its neutralising the free acids in the soil and 

 rendering the plant food constituents suitable for absorption 

 by the plant. Mr. H. B. Hutchinson's experiments, however 

 (Journ. Agric. Science, 1913, V, 320), indicate that these 

 effects do not explain the whole of the results obtained in 

 practice through the application of lime to the soil. The 

 germicidal action of the lime is a material factor, and it has 

 been found that its action in this direction is more pronounced 

 than that of volatile antiseptic agents, but is less effective 

 than sterilising the soil by heat. The immediate effect of 

 adding lime is to destroy the larger protozoa and a large 

 proportion of the bacteria in the soil, and to decompose 

 organic nitrogenous compounds. After the whole of the lime 

 has been transformed into carbonate bacteria begin to develop 

 rapidly, and there is an increase in the production of available 

 plant foods. 



These conclusions were confirmed by the results of 

 practical tests with different soils. For example, the addition 

 of 0-5 per cent, of caustic lime to a poor soil already con- 

 taining sufficient calcium carbonate was followed by a 

 pronounced increase in the crops ; while treatment of a good 

 garden soil with varying proportions of caustic lime up to 

 1 per cent, caused the first crop to be poorer, but the second 

 crop to be much richer than originally. 



THE ACTIVE MODIFICATION OF NITROGEN.— 

 It has been asserted that the phenomena attributed to active 

 nitrogen are due to the presence of traces of oxygen, but the 

 Hon. R. J. Strutt shows (Proc. Royal Soc, 1913, A. 

 LXXXVIII, 539) that this is not the case. On the contrary, 

 oxygen has an unfavourable effect, and when present in the 

 proportion of two per cent, inhibits the reactions of the 

 nitrogen. In preparing the nitrogen for the action of the 

 electric discharge, Mr. Strutt absorbs all traces of oxygen by 

 means of phosphorus, and then dries the gas by passing it 

 first through phosphorus pentoxide and then through a tube 

 packed with copper gauze and cooled with liquid air. Finally, 

 oxides of phosphorus are dissolved by the water which rises 

 in the gas-holder, the latter being meanwhile covered with 

 black cloth to prevent the action of light upon the nitrogen. 



Nitrogen thus purified and rendered active by the passage 

 of an electric discharge will combine with vaporised zinc, 

 cadmium, mercury, sulphur, and other elements to form 

 nitrides, which are decomposed by water, with the liberation 

 of ammonia. It reacts with carbon bisulphide to produce a 

 blue polymerised carbon monosulphide and a blue nitrogen 

 sulphide, while it decomposes sulphur chloride with the 

 formation of the ordinary yellow nitrogen sulphide. It appears 

 to act upon most organic compounds, liberating hydrocyanic 

 acid, but carbon tetrachloride is not decomposed in this way. 



ACTION OF OZONE ON FIBRES.— The results of 

 experiments to determine the effect of ozone upon different 

 textile fibres are described by Mr. C. Doree in the Journ. Soc. 

 Dyers and Col., 1913, XXIX, 205. In each case the yarns 

 were exposed to the action of oxygen containing 1-5 to 2 per 

 cent, of ozone and their relative breaking strength and 

 elongation determined after various periods. In the case of 

 cotton and artificial silk there was but little reduction in the 

 strength during the first hour, but subsequently the deteriora- 

 tion was very rapid, and after twelve hours the breaking 

 strength had fallen from 30 to 50 per cent. This alteration 

 in the physical properties was accompanied by a chemical 

 change. For example, a sample of cotton-wool, containing 

 44-4 per cent, of carbon, showed only 43-5 percent, after the 

 oxidation. Flax was attacked much more rapidly than cotton, 

 and yielded formic acid and solid acids, but dry wool was 

 hardly affected after several hours' exposure to ozone in the 

 presence of moisture. If the wool were first soaked in water, 

 however, a rapid decrease in its strength and elongation was 

 observed, while silk under similar conditions was rapidly 

 attacked by ozone. 



