568 



NATURE 



[January 29, 1920 



mental power are shown not only in hybrids, but 

 also in pure species. By removing their eggs when 

 laid, the birds can be overworked in reproductive 

 activity, with a corresponding decrease in energy 

 of the offspring. The .result is more females and 

 a shorter term of life. Even in normal reproduc- 

 tion there is found to be a gradual diminution in 

 developmental power of the germs throughout the 

 season. 



This idea of relative and varying germinal weak- 

 ness and strength runs through all the work, and 

 will be found difficult to controvert. It is prob- 

 ably but the beginning of a theory of evolution 

 founded primarily, not on morphological, but on 

 energy conceptions. 



(6) Another important relationship which was 

 studied in great detail is that between fertility and' 

 sex. The problems involved are too many-sided 

 to discuss here. It was found, for example, that 

 while in crosses between closely related species 

 the sexes appear in equal numbers, in inter- 



FlG. 5. — The Japanese turtle-dove, Turtur 

 orientals. Believed to represent the primitive 

 colour pattern in pigeons, from which the 

 chequers ot C. iivia were developed by the 

 disappearance of pigment along shalt 6f feather. 



family crosses only or chiefly males are produced. 

 In wide crosses the development may only begin, 

 or it may stop at any stage between hatching and 

 maturity, resulting in short-lived birds. All these 

 and many other results are interpreted in terms of 

 developmental energy, the difference between the 

 sexes being regarded as essentially a difference 

 in metabolic level. This view is in accord with 

 the classical theory of sex of Geddes and .Thom- 

 son. Some means must be found of harmonising 

 it with the chromosome theory. 



(7) The study of voice, instincts, and behaviour 

 in pigeons has added much to the value of the 

 whole work. Whitman's intimate knowledge of 

 pigeons from this side frequently furnishes cor- 

 roborative evidence of relationships. It also 

 made possible his singular success in crc*sing 

 many species which had never been crossed before. 

 The differences in the instincts of the reproductive 

 cycle are often surprisingly marked and definite 

 in. different species. In a discussion of instinct in 

 NO. 2622, VOL. 104] 



relation to intelligence, the author's view is that 

 as instincts become more complex and plastic 

 the possibility of choice finally enters, so that 

 without any added brain structure the organism is 

 encouraged or constrained by circumstances to 

 learn to use its privilege of choice. 



These notable volumes, two of which are 

 sumptuously illustrated with coloured plates by 

 Japanese artists, will doubtless arouse much dis- 

 cussion. It is to be regretted that an index has 

 not been added, to make their contents more 

 readily available. R. R. G. 



THE NITROGEX PROBLEM.^ 

 II. 



BEFORE the war the United Kingdom produced 

 and exported large quantities of ammonia 

 nitrogen, upwards of 70 per cent, of the home 

 production being, in fact, exported. Indeed, the 

 British export trade in ammonium sulphate was 

 larger than that of any other country. On the 

 other hand, she was entirely dependent upon the 

 Chile product for her nitric nitrogen. Agriculture 

 accounted for the major portion of the home con- 

 sumption of fixed nitrogen, but this only repre- 

 sented 235 per cent, of the total home production 

 and importation. Indeed, in proportion to the 

 total area under cultivation, the United Kingdom 

 uses less artificial nitrogenous fertilisers than any 

 other progressive agricultural country. 



The war has had a serious effect upon the home 

 industry. Whereas the estimated output of by- 

 product ammonia in America and of by-product 

 and synthetic ammonia in Germany in 191 7 was 

 more than double what it was in 191 3, with us it 

 declined in 1914 and 1915, slightly recovered in 



1916, and in 1917 showed only an increase of 

 6 per cent, over the amount in 1913. Our export 

 trade in ammonium sulphate practically ceased in 



1917. Countries which formerly imported our 

 sulphate of ammonia are now making their own 

 by-product ammonia. This result is due to the 

 action of the Government in controlling the export 

 and price. -As is well known, there has been a 

 remarkable development in agriculture in this 

 country during the last; four years, and the Jiome 

 demand for nitrogenous fertilisers has been in 

 excess of the supply. There can be no doubt that 

 both the industrial and the agricultural demand for 

 nitrogen products will continue to increase. The 

 Committee estimates that on the assumption that 

 the present scale of food production is at least main- 

 tained, the demand in the near future will prob- 

 ably represent a quadrupling of the average pre- 

 war requirements. Our export trade in ammonia 

 fertilisers will have in future to reckon to a still 

 greater extent with synthetic products. It can 

 only successfully compete by this country itself 

 manufacturing such products. No doubt 

 economies and improvements in existing by-pro- 

 duct processes are conceivable and possible, but 



1 " Ministry of Munitions of War. ^!unitions Inventions Department.' 

 Nitrogen Products rommittee. Final Report." Pp. vi+357. (London: 

 H.M. Stationery Office, 1919.) Cmd. 482. Price 4^. nel. Continued from 

 P 535. 



i 



