November 4, 1920] 



NATURE 



305 



of the agricultural section (chap, v.) is the pro- 

 posal to base the legal classification of land upon 

 indicator communities. The bearing of the study 

 of climatic cycles on agricultural practice is dealt 

 with in the light of facts already for the most part 

 summarised in "Plant Succession." The large 

 amount of space devoted to grazing-indicators 

 (chap, vi., 66 pages) is accounted for partly by the 

 very full discussion of over-grazing, in the detec- 

 tion of which condition indicator-species appear 

 to be specially helpful, and partly by a digression 

 on the general principles of range [ranch] im- 

 provement. As regards the forestry section 

 (chap, vii.), the very scant attention paid to 

 afforestation is disappointing to the European 

 reader, though comprehensible in view of the 

 relatively large area of natural forest growth still 

 preserved intact in North America. 



In order properly to appreciate Dr. Clements's 

 arguments, it is above all necessary to under- 

 stand his point of view, which is that of a 

 thorough -going adaptationist who regards every 

 feature in the behaviour or structure of an 

 organism as a resfjonse to environment. His 

 utmost concession to the influence of heredity is 

 the admission that " structure also possesses a 

 well-known inertia, as the result of which it may 

 register the impact of factors but partially or 

 slightly." Probably few biologists will be satis- 

 fied with so meagre an allowance for the factor of 

 inherited constitution. Further, for Dr. Clements, 

 '■(■oology is the central and vital part of botany," 

 and other lines of botanical research are, or ought 

 to be, subordinated thereto. One need not, there- 

 fore, be surprised to meet with sweeping pro- 

 posals for the radical reform of taxonomy, in- 

 volving the institution of a trinomial nomen- 

 clature [!] and the virtual abolition of the use of 

 herbarium type-specimens. Unless we are pre- 

 pared to jettison the taxonomic work of the past 

 centuries in its entirety, it is to be feared that 

 a hasty acceptance of such revolutionary sugges- 

 tions would increase rather than diminish the diffi- 

 culties that already beset the taxonomist and all 

 who depend upon him. Doubtless "the practical 

 man is [or would like to be] concerned primarily 

 with real species rather than with the many varie- 

 ties and forms into which some of them fall " ; 

 but the problem of what are " real species " 

 remains to be solved, and surely this desirable 

 end is more likely to be attained through a 

 healthy co-operation among workers in the various 

 branches of biology than by a lour de force in any 

 one of them. 



Apart from such debatable matter, "Plant In- 

 dicators" U a reicord of a large quantity of solid 

 NO. 2662, VOL. 106] 



observation and experiment, and a stimulating 

 book with a wider appeal than that of the average 

 ecological rnemoir. Judgment as to the practical 

 value of the indicator method must be suspended 

 until it has undergone the test of extensive 

 application under varied conditions and on an 

 economic footing. 



Dr. Clements properly lays stress on the special 

 value of ecological research in new or partly 

 settled regions. Oddly enough, no mention is 

 made of those tropical countries which in every 

 respect offer the most promising field to the 

 ecologist, and to which American botanists have 

 unrivalled facility of access. M. D. 



The Food Problem of the United States. 



The Nation's Food: A Statistical Study of a 

 Physiological and Social Problem. By Prof. 

 Raymond Pearl. Pp. 274. (Philadelphia and 

 London : W. B< Saunders Co., 1920.) Price 

 16s. net. 



ONE result of the Great War has been to bring 

 into unusual prominence the problem of the 

 world's food supply. Each civilised nation con- 

 tains two great divisions, which in many ways are 

 somewhat antagonistic, dependent respectively on 

 food production and on industrial work. The 

 problem differs in urgency for the two groups : 

 for the food producer, living in the country, it is 

 one of greater or smaller profits, but not of daily 

 bread, of which he is certain; for the industrial 

 town-dweller the problem is more serious, because 

 the intricate social machine is easily thrown out 

 of gear by a few disaffected spirits, and food is 

 forthcoming only so long as the machine turns 

 out sufficient goods to induce the production of 

 more food than the countryman needs for his own 

 consumption. 



Prof. Raymond Pearl has given in this book a 

 statistical study of the food problem of the United 

 States, and with his usual thoroughness and 

 breadth of view he has included in his inquiry so 

 many ramifications that his investigation covers 

 Europe also. It thus possesses extraordinary in- 

 terest at the present time. His tables contain a 

 •wealth of material of -which only a few indica- 

 tions can be given here. The contribution made 

 by the United States to the food supply of the 

 Allies during the war was remarkable. The pre- 

 war average export of wheat and flour was 1227 

 million bushels, of which 433 million went to the 

 Western Allies ; during the war, but before 

 America's entry, it rose to 2629 million bushels, 

 of which 15 1 2 million went to the Allies; even in 

 the first Jrear of the war the AHiet still received 



