September 9, 1922] 



NA TURE 



555 



physiological laws must be reckoned with as an 

 essential factor in industrialism. Attention was 

 directed to the tremendous annual loss in time due to 

 sickness and disability, and it was pointed out that 

 primarily this wastage could not be charged to man 

 being of unsuitable design for the work he was called 

 upon to perform ; on the contrary, the physiological 

 balance of the organism was beautifully designed to meet 

 most varying strains. After reference to the relation 

 of the various systems, respiratory, circulatory, etc., 

 to the maintenance of efficiency, Prof. Cathcart went 

 on to discuss the factors which, in his opinion, play 

 the predominant roles in the maintenance of maximum 

 efficiency. He believed that there were, at least, four 

 intrinsic factors, i.e. factors directly related to muscle 

 movement — (a) the rate of the performance of the 

 work, (b) the amount of rest offered to or taken by 

 the subject, (c) the rhythm with which the work was 

 performed, and (d) the work habits developed by the 

 worker. He reviewed each of these factors in turn; 

 the influence of load and the type of work (positive 

 and static) was dealt with under the rate of perform- 

 ance, and the formation of conditioned reflexes in 

 connexion with rhythm and habit. The more extrinsic 

 factors, i.e. those less directly related to muscle effort, 

 were next discussed, including the influence of t In- 

 state of nutrition and the nature of the food supplied, 

 of the work environment, and the psychic factor 

 generally, particular reference being made to monotony 

 of occupation and the part played by the temperament 

 of the worker. Other still more extrinsic factors like 

 housing, personal habits, lighting, heating, ventilation, 

 etc., were also mentioned. The general conclusion 

 reached was that although the real over-all efficiencv of 

 the worker could not be causally related to any single 

 factor, further scientific investigation along physio- 

 logical lines, with the mutual co-operation of the 

 employer, employee, and scientific worker, would throw 

 much light on this most difficult and vitally important 

 problem. 



Transport of Organic Substances in Plants. 



The address to Section K (Botany), by Prof. H. 11. 

 Dixon, dealt with the transport of organic substances 

 in plants. Organic substances are conveyed upwards 

 in the rising transpiration and root-pressure currents. 

 The transport is probably mainly effected in the 

 tracheae of the outer layers of the wood. Ringing may 

 block these channels completely or partially by the 

 introduction of air-bubbles and by exudations from 

 injured cells into the lumina and walls of the tracheae. 



The downward transport of these substances from the 

 leaves to the lower parts of the plant is usually assigned 

 to the bast, although there is weighty experimental 

 evidence that living conduits are not essential. Cal- 

 culation shows that if the bast were used as the conduit 

 a velocity of flow in it of about 50 cm. per hour would 

 be required. In such narrow tubes as the bast is 

 composed of, with frequent cross partitions and colloid 

 contents, this velocity seems quite impossible. These 

 considerations render it highly probable that the 

 trachea of the wood are the path for downward trans- 

 port also. There is ample experimental evidence for 

 downward as well as upward movement of sap in the 



NO. 2758, VOL. I IO] 



tracheae: Tension in the sap determines a flow from 

 any source above or below. Resistance to transverse 

 flow in the wood practically subdivides that tissue into 

 a number of longitudinal filaments of tracheae con- 

 nected anatomically at various levels in the plant. 

 Transpiration from the upper end of one filament may 

 thus lead to a downward motion in a neighbouring one. 



There is also conclusive evidence for this reversed 

 motion in intact normal plants. 



Recent work has shown that the transfer of 

 stimuli from the receptive to the motile regions of 

 plants is effected by the passage of hormones. In 

 several cases it is certain that the hormones are con- 

 veyed in the transpiration current. Moreover, the 

 movement is often basipetal. Such a downward flow 

 is clearly available for the conveyance of organic food- 

 stuffs as well as hormones. Local increases in the 

 permeability of leaf-cells will allow solutions of organic 

 substances to pass into the tracheae. The tension 

 generated in the sap by the transpiration of other leaf- 

 cells will draw this solution downwards in the tracheae. 

 Experimental evidence for this method of transport is 

 available. The volume-changes of leaves and parts 

 of leaves observed during transpiration are in all 

 probability the result of these changes in permeabilitv, 

 and are directly connected with the supply of organic 

 substance from the leaf-cells to the transpiration- 

 current for downward transport. 



Educational and School Science. 



Sir Richard Gregory's address as president of 

 Section L (Educational Science) was a statement 

 of the biological basis of education and a plea for 

 broader conceptions of the scope and substance of 

 science teaching in schools. It is the business of 

 education to promote the right adjustment between 

 the developing human organism and its surroundings, 

 and this implies that the nourishment provided at all 

 stages of growth should be not only such as supplies the 

 needs of the moment but also builds up strength to 

 live a full life under the conditions of the times. School 

 instruction in science is not, therefore, intended to 

 prepare for vocations, but to equip pupils for life as it 

 is and as it soon may be. It is as essential for intelli- 

 gent general reading as it is for everyday practical 

 needs ; no education can be complete or liberal without 

 some knowledge of its aims, methods, and results, and 

 no pupil in primary or secondary schools should be 

 deprived of the stimulating lessons it affords. In such 

 schools, however, the science to be taught should be 

 science forall,and not for embryonic engineers, chemists, 

 or even biologists ; it should be science as part of a 

 general education — unspecialised, therefore, and with- 

 out reference to prospective occupation or profession, 

 or direct connexion with possible university courses 

 to follow. There is very present need for the reminder 

 that science is not all measurement, nor is all measure- 

 ment science. In the great majority of secondary 

 schools science signifies chiefly quantitative work in 

 physics and chemistry — laboratory exercises and 

 lessons based upon them — and rarely is any attempt 

 made to show the pupils what a wonderful world we 

 live in, or what science has done, and is doing, for them 

 in everyday life. By the prevailing obsession in regard 



