362 



SCIENCE 



[N. S. Vol. L. No. 1294 



nock, where a good load factor may be 

 found in a small area, -but in this case the 

 consumers are chiefly mills, which require 

 current for many hours daily. 



There is no golden rule to secure cheap 

 electricity. The most favorable size, local- 

 ity and number of generating stations in 

 each area can only be arrived at by a 

 close study of the local conditions, but 

 there is no doubt that, generally speaking, 

 to secure cheap electricity a widespread 

 network of mains is in most cases a very 

 important, if not an essential, factor. 



The electrification of tramways and sub- 

 urban railways has been an undoubted 

 success where the volume of traffic has 

 justified a frequent service, and it has been 

 remarkable that where suburbaxi lines have 

 been worked by frequent and fast elec- 

 trical trains there has resulted a great 

 growth of passenger traffic. The electrifi- 

 cation of main-line railways would no 

 doubt result in a saving of coal; at the 

 same time, the economical success would 

 largely depend on the broader question as 

 to whether the volume of the traffic would 

 suffice to pay the worMng expenses and 

 provide a satisfactory return on the 

 capital. 



Municipal and company generating sta- 

 tions have been nearly doubled in capacity 

 during the war to meet the demand from 

 munition works, steel works, chemical 

 works, and for many other purposes. The 

 provision of this increased supply was an 

 enormous help in the production of ade- 

 quate munitions. At the commencement 

 of the war there were few steel electric 

 furnaces in the country; at the end of last 

 year 117 were at work, producing 20,000 

 tons of steel per month, consisting chiefly 

 of high-grade ferro alloys used in muni- 

 tions. 



Charles A. Parsons 

 (To be concluded) 



PHYSIOLOGICAL ISOLATION BY LOW 



TEMPERATURE IN BRYOPHYLLUM 

 AND OTHER PLANTS 



In axiate plants a physiologically active 

 growing' tip inhibits more or less completely 

 the development of other growing tips or axes 

 of the same plant within a certain distance 

 which varies to some extent with the intensity 

 of physiological or metabolic activity in the 

 inhibiting tip. This physiological correlation 

 is not specific for the growing tips of stems 

 and roots, but other parts of the plant, e. g., 

 leaves, may exert the same inhibiting effect 

 to a greater or less degree. Removal of the 

 growing tip or other inhibiting part, or a 

 sufficient decrease in its metabolic activity 

 abolishes its inhibiting action upon other 

 parts. These facts have long been known, 

 much experimental work has been done upon 

 this problem of physiological correlation and 

 various hypotheses have been advanced. As 

 regards the manner in which such an effect 

 of one part upon another at a greater or less 

 distance may conceivably be produced, there 

 are apparently three possibilities : first, the 

 growing tip may inhibit indirectly by obtain- 

 ing through its greater physiological activity 

 the greater proportion of nutritive materials 

 necessary for growth and development ; second, 

 the growing tip or other inhibiting part may 

 produce substances which are transported by 

 the fluids of the plant and which exert a 

 specific inhibiting effect upon other parts; 

 and third, the metabolic activity of the grow- 

 ing tip may produce dynamic changes which 

 are conducted through the protoplasm of the 

 plant and influence the physiological condition 

 of the parts which they reach. 



As regards the first of these possibilities it 

 is difficult to conceive how in the bean seed- 

 ling, to take a concrete case, the growing tip 

 can so completely deprive the buds in the axils 

 of the cotyledons of nutrition that they are 

 unable to grow at all, although they are very 

 much nearer the source of both inorganic and 

 organic nutrition than the tip. The attempt 

 to interpret this inhibition solely in nutritive 

 terms has proven unsatisfactory. 



The second possibility, the production of 



