April 27, 191 1] 



NATURE 



27; 



that the farmer has been dependent upon the re- 

 sources of the soil alone. In Europe, however, the 

 cultivator has been forced by the lack of further land 

 to a system of conservative farming which would 

 maintain the fertility of the soil and the production 

 of crops, at a somewhat low level, perhaps, but one 

 r that would show no decline for a very long period of 

 lime. 



In the Norfolk four-course rotation, for example, all 

 hat is sold away from the farm is meat and corn ; the 

 -traw, the hay, and the roots are more or less com- 

 pletely returned to the soil. The growth of the clover 

 crop once in the rotation was more than capable of 

 replacint^ the nitrogen sold awa}- and the inevitable 

 wastage. The stock of potash In the soil is so enor- 

 mous as to be practically inexhaustible, and cultiva- 

 ! tion will slowly make it available. Only the phos- 

 phoric acid suffers a steady and irreplaceable loss under 

 -uch a conservative system of farming, but this loss 

 is not a very large one. Prof. Hopkins has made it 

 his mission to awaken the Illinois farmer and his 

 neighbours east of the Mississippi to a sense of the 

 inevitable decline of the fertility of their land unless 

 they also work out a similar conservative rotation, 

 and he has shown them how this can most profitably 

 he effected with the fertilising resources now avail- 

 able. 



In his system Prof. Hopkins lays less stress upon 

 the nitrogen question than we are accustomed to do 

 in Europe. Even to-day the old prairie lands are 

 till rich in nitrogen, and he considers that the in- 

 roduction of a vigorous clover or cow. pea crop into 

 lie rotation will be sufficient to maintain the nitrogen 

 r a profitable level for production. To secure a good 

 lover crop it is necessary that there should be an 

 iinple supply of phosphoric acid and potash. Of the 

 atter element the initial stock is large enough to last 

 or many generations ; all that is necessary is to 

 ring it steadily into solution. To this end, and also 

 o ensure the proper bacterial actions which both 

 ollect nitrogen and bring the organic nitrogen com- 

 lounds in the soil into forms assimilable by plants, a 

 leutral reaction is required in the soil, and Prof. 

 I lopkins uses finely ground limestone in preference 

 io the quick-lime which we more commonly employ. 

 Then he turns to the phosphoric acid to complete the 

 liain, and supplies this fundamental element by one 

 f the mineral phosphates so abundant in Carolina 

 or Florida in a finely ground condition, preferring 

 the neutral finely ground rock to the artificially pre- 

 pared acid superphosphates more common in Europe. 

 To Prof. Hopkins the ground phosphate is the kev- 

 stone of the arch. The carbonate of lime i^ in ( os- 

 snry to prepare the ground and to liberate fhc potash, 

 but the phosphoric acid provides the item tliat was 

 n( ( e-.-..-irv for fertility, not only to the tj;rain crops 

 tlienisehcs, but to the nodule bacteria on tlie clover, 

 whicli li i\e to maintain the stock of nitrogen. Prof. 

 Mopkiii-. lia-- (leinonslrated the success of his system 

 [)erinii ntally at Urbana, and on manv a farm in 

 lilinoi-^, and has taken up the propaganda of this 

 nielliod of ic~,toriiiL;- lli'' \\:inin;> fiililii\ of the older 

 lands of the United States with iht; iva\\ and con- 

 NO. 2165, VOL. 86] 



viction of a missionary. In this cause he has been 

 brought into sharp conflict with the opinions that 

 have issued from the Division of Soils at Washing- 

 ton, where Whitney and Cameron have put out their 

 theory, which in its crude form as summarised for 

 popular consumption, would seem to say that all soils 

 are inexhaustible and equally rich as regards their 

 mineral constituents, and that nothing is more re- 

 quired for fertility than a proper rotation and due 

 attention to the conservation of the water supply, ex- 

 penditure upon fertilisers being in the main unneces- 

 sary. 



On the value of this theory and its application to 

 practice this is not the place to enter, but the book 

 before us is to a large extent a detailed statement of 

 Prof. Hopkins's position and the justification of his 

 belief in fertilisers, mOre particularly in ground lime- 

 stone and rock phosphate, as a means of raising the 

 level of productiveness in the United States. 



Prof. Hopkins's book is designed on rather different 

 lines from the usual treatise on agricultural chem- 

 istry, or even upon soils. After a general introduction 

 on the elements of plant nutrition, he discusses in 

 some detail the types of soils to be met with In the 

 United States, and then goes on to develop his sys- 

 tem of agriculture with an account of the materials 

 necessary to maintain fertility. Here the reader will 

 find a number of experimental data concerning the 

 value of ground limestone in comparison with lime, 

 and particularly of ground rock phosphate as against 

 superphosphates and other manufactured fertilisers. 



After a chapter of polemics on the theory of soil 

 fertility, Prof. Hopkins proceeds to discuss field ex- 

 periments, taking the Rothamsted experiments as a 

 type of what may be expected under European con- 

 ditions, and then summarising in a very convenient 

 and interesting form for the European reader the 

 work that has been done in Pennsylvania, Ohio, Illi- 

 nois, Minnesota, and other American States. 

 Though the book Is written for the educated farmer, 

 on this side of the Atlantic it is rather to the teacher 

 and student that It will appeal, because our farmers 

 will be strange to the conditions which render its 

 main argument of so much importance. To the 

 teacher, however, It is a mine of information ; as it 

 is also written with such vigour and refreshing con- 

 viction of the fundamental importance of its doefrine. 

 we can well understand how Prof. Hopkins lias be- 

 come one of the really inspiriting forces in American 

 agriculture. A. D. H. 



THE TERMITES OF CEYLON. 



Termitenh hi I! ant ('cyh'n. iii-uf Slii,Iii-}i ^ur '-' 



der Ti' •"■'^■icJi riii Knpili'l l\ .'loiiiiili i i ;.;- 



entonio I'ml K. I'',vrliciieli, Pp. \\\ii ! 



263.2 pis. and 08 tigurcs in the text. Jena : Giistav 

 Fischer, iqii.) Price 6.50 marks. 



THE teiniiies (or white ants, as they are frcHjiientJv 

 liunii^li improperly cnlied), alihoui^Ii thev belong 

 to the order Neuropt(>ra, I'xei r(lin-l\- r<^vrmlile ilic 

 true ants in their hablt>, and are of ahiiost e(.|ual in- 

 terest, 'i'liev are, however, troi)ieal iii'-i'ii^, .hkI ia- 

 tremely destructive, and aIthoiiL;h one species has 



