52 



KNOWLEDGE. 



February, 1915. 



voltage and with electric discharge at liigh tensions. The 

 results show that direct currents have no effect on the 

 respiration of peas other than that due to accompanying 

 changes of temperature ; but the proportion of these cur- 

 rents actually traversing the peas was probably very small, 

 the majority being taken by the water films of the seeds. 

 Overhead discharge of low density has no effect on respir- 

 ation ; but with liigher currents a definite increase of the 

 carbon dioxide output was observed, this increase being 

 wholly attributable to the rise of temperature caused by 

 the discharge. In the field, where the currents are too 

 small to produce any appreciable rise in temperature, 

 electrification will have no effect on respiration, and an 

 explanation of the acceleration of growth must be sought 

 in other functions of the plant. The gaseous products of 

 the discharge in air have no effect on germinating peas, 

 but are injurious to young seedlings. These results do not, 

 of course, mean that the acceleration is inexplicable, for 

 one result of electrification may be increased transpiration, 

 which alone would account for a more rapid attainment of 

 maturity by the plant ; while various observers have found 

 that electrification produces increased activity of con- 

 structive metabolism — the processes of building up food 

 materials in the plants. 



STATISTICAL METHODS IN PLANT GEOGRAPHY. 

 — For many years the Swiss botanist Jaccard has been 

 investigating in great detail the distribution of plants in 

 certain definite areas in alpine meadows, and has obtained 

 some interesting results, which appear likely to be of general 

 application. His latest paper (Rev. gin. Bot., Volume 

 XXVI) deals with the vegetation of some alpine gravel 

 areas, but a fuller account of his earlier results is given 

 in an English paper (New Phytologist, Volume XI). Having 

 made a census of the flowering plants growing in the areas 

 to be compared — similarly situated localities of about the 

 same area in different parts of the Alps — he applies to the 

 analysis of his results what he called the " coefficient of 

 community," that is, the percentage ratio between the 

 number of species common to two district and the total 

 number of species in the two districts. For alpine meadows 

 he found that (1) the value of this coefficient does not 

 depend on floral richness, but upon the ecological characters 

 of the areas studied ; (2) the alpine flora is extremely diverse 

 in floristic composition ; (3) the rare species are most 

 numerous and the common species least numerous [This 

 does not apply to individuals, but to species] ; (4) the 

 coefficient is usually higher for contiguous than for distant 

 areas. He also uses what he terms the " generic coefficient," 

 that is, percentage ratio between number of genera and 

 number of species, and finds that this coefficient varies 

 inversely with the variety of ecological conditions in the 

 areas compared. For instance, in alpine areas its value 

 increases with altitude ; while in the Belgian sand-dunes 

 (from data given by Massart) it is greatest (100) under the 

 excessive and narrow ecological limits of the moving 

 dunes, and least (73) under the more varied conditions of 

 the pannes (salt marshes). From his analyses Jaccard 

 draws the following general conclusions. The distribution 

 of plants, at any rate in the alpine zone, is a resultant of 

 the combined action of three kinds of factors : ecological 

 biological (degree of adaptation), and sociological (com- 

 petition between species). The action of these factors 

 has resulted in two kinds of selection : an eliminative 

 selection of species and a distributive selection, determining 

 the number of individuals and the nature of associated 

 species. Readers interested in the subject should consult 

 the New Phytologist paper for details of Jaccard 's interesting 

 investigations. 



A DARK-GROUND ILLUMINATION STUDY OF 

 PLANT CELLS. — Until about ten years ago the method 

 of dark-ground illumination with the microscope was 

 regarded simply as a means of exhibiting objects with 

 pretty and striking effect, and even now much less use has 

 been made of the method in the investigation of the plant 



cell than might have been anticipated. In a recent paper 

 Price (Annals of Botany, Volume XXVIII) gives the 

 results of his examination of various plant cells, made with 

 the object of seeing whether, by this method, more facts 

 might be obtained concerning the colloid structure of the 

 living and the dead cell and the reactions of the colloid. He 

 gives a brief account of the necessary procedure, suitable 

 objects for study, and so on, and the paper will be found 

 very useful by others wishing to examine plant cells by 

 this method. The objects used were chiefly filamentous 

 algae, spores, and hairs ; and in his summary the author 

 points out that the method often reveals new structural 

 features, and is useful in establishing the presence of 

 minute particles, which are difficult to see or are unresolved 

 in direct illumination, though the method is restricted in 

 application, owing to the difficulty of selecting suitable 

 material for examination. It is generally recognised that 

 protoplasm is a colloidal complex existing both in the 

 hydrosol and the hydrogel state, a hydrosol being a colloidal 

 solution — differing from an ordinary solution essentially 

 in consisting of particles suspended in a continuous medium 

 — while a " gel " is a sponge-like body in which the con- 

 tinuous phase encloses the other phase in a mesh of cavities. 

 To a certain extent, these states are spontaneously reversible. 

 The process of germination of certain fungus spores showed 

 the gradual conversion of the gel - contents of the spore 

 into a hydrosol on absorption of water, while later on 

 a formation of a gel may occur again. The nucleus and 

 chloroplast are evidently specialised parts of the plasma, 

 with a hydrogel structure ; particles and vesicular bodies 

 (" sap particles "), usually present in the cell-sap and 

 showing a continuous Brownian movement, were found 

 to increase in number with decreasing vitality of the cell. 

 The effects of plasmolysis were studied with different 

 reagents, and it was found possible to distinguish an outer 

 layer with much finer structure than the rest of the proto- 

 plasm, this layer being apparently the part concerned in 

 the formation of the fine fibrils, which often connect the 

 plasmolysed protoplast with the wall of the cell. A similar 

 layer was also recognised on the inside of the protoplast 

 against the vacuole. The action of fixing and coagulating 

 agents was studied, and it was found that during fi.xation 

 a change to an opalescent hydrogel takes place, the rate 

 of formation and the structure of the gel differing in different 

 plant material and with different agents. 



CHEMISTRY. 



By C. AiNSWoRTH MircHELL, B.A. (Oxon), F.I.C. 



GERMANY'S MOTOR FUEL —Three recent issues of 

 the Zeitschrift fur angewandte Cliemie which have recently 

 come to hand by way of a neutral country show the straits 

 to which Germany has already arrived from the shortage 

 of petrol. 



According to Dr. Hempel (page 521), Germany, in 1913, 

 produced 179,800 tons of petrol and 160,000 tons of benzene 

 (benzol), nearly a third of which was exported to France, 

 while in the year 1912-13 the country's production of 

 alcohol — mainly from potato starch — reached 3,753,265 

 hectolitres. Alcohol thus appears to be the natural sub- 

 stitute for petrol, and Dr. Hempel states that, by order of 

 the Kaiser, all motor-cars in Berlin have been adapted to 

 use alcohol as well as petrol. 



The relative heats of combustion of the various possible 

 fuels are as follows : Petrol, 9500 to 10,500 ; pure benzene, 

 10,260 ; commercial benzene (benzol), 9550 to 10,000 ; 

 pure alcohol, 7402 ; ninety-five per cent, alcohol, 5875 ; 

 and pure naphthalene, 9628-3 calories per kilogramme. 



In practice a mixture of four parts of ninety-five 

 per cent, alcohol with one part of benzene, containing 

 two hundred grammes of naphthalene per htre, gave 

 the same results as ordinary petrol ; whereas the use of 

 alcohol by itself tended to rust the tubes of the carburettor. 



