Scientific Agriculture. 



44 



[July, 190^. 



last he proves from the Rothamsted 

 experiments which have shown " that 

 wheat can be grown continuously upon 

 the same land for more than fifty years, 

 and that the yield when proper ferti- 

 lizers are applied remains as large in tbe 

 later as in the earlier years of the 

 series. . . . Mangolds. . . . show no 

 falling off in yield tboughthey bave now 

 been grown upon tbe same land for 

 thirty-two years." 



Nevertheless the "sickness" of land 

 continuously under one crop is a fact 

 which the Rothamsted experiments 

 undoubtedly confirm, and Mr. Hall is 

 prompt to admit it. There is some 

 positive evidence that " most plants — 

 some to a very slight degree, like wheat, 

 and mangolds, others markedly, like 

 clover, turnips and flax— effect some 

 change in the soil whicli unfits it for the 

 renewed growth of the crop," and this 

 injurious factor may be, Mr. Hall thinks, 

 "either the excreted toxins of Whitney's 

 theory or may be some secondary effects 

 due to the competition of injurious 

 products of the bacteria and other micro- 

 flora accumulating in the particular soil 

 layer in which the roots of the crop 

 chiefly reside." But " as it stands at 

 present Whitney's theory must be re- 

 garded as lacking the necessary experi- 

 mental foundation, no convincing evi- 

 dence has been produced of the funda- 

 mental fact of the excretion of toxic 

 substances from plants beyond the 

 autotrophic seedling stage, nor is there 

 direct proof of the initial supposition 

 that all soils give rise to soil solutions 



sufficiently rich in the elements of plant 

 food to nourish a full crop did not some 

 other factor come into play." 



" If, however, we give the theory a 

 wider form, and, instead of excretions 

 from the plant, understand debris of any 

 kind left behind by the plant and the 

 results of bacterial action upon it, we 

 may thereby obtain a clue to certain 

 phenomena at present imperfectly under- 

 stood. The value of a rotation of crops 

 is undoubted, and in the main is expli- 

 cable by the opportunity it affords of 

 cleaning the ground, the freedom from 

 any accumulation of weeds, insect or 

 fungoid pests associated with a parti- 

 cular crop, and to the successive tillage 

 of different layers of the soil, but for 

 many crops there remains a certain 

 beneficial effect from a rotation beyond 

 the factors enumerated." That the clue 

 lies in " disinfection " of some kind would 

 seem to be indicated by Mr. Hall ; who 

 in his closing remarks draws attention 

 to the increase of fertility which follows 

 partial sterilization of the soil either by 

 heating or by the use of volatile anti- 

 septics such as toluene or carbon bisul- 

 phide. But he concludes with a warning 

 which may well be taken as a " word to 

 the wise. " "The soil," he says finally, 

 "is such a complex medium— the seat 

 of so many and diverse interactions, 

 chemical, physical and biological— and is 

 so unsusceptible of synthetic reproduc- 

 tion from known materials, that experi- 

 mental work of a crucial character 

 becomes extremely difficult, and above 

 all required to be interpreted with 

 extreme caution and conservatism." 



MISCELLANEOUS. 



LITERATURE OP ECONOMIC 

 BOTANY AND AGRICULTURE. 



By J. C. Willis, 



Cardamoms.— 



Cardamom cultivation in Travan- 

 core. " T. A." Jan. 1906, p. 835. 



Cardamom cultivation in South 

 Mysore. Ind. Forester. Nov. 1908, 

 p. 657. 



Cassava.— 



Tapioca as a catch crop. Str. Bull, 

 1900, pp. 133, 223. 



Cassava trials. Jamaica Bull. 1906, 

 p. 73. 



Eene biolohische bereidiugsmethode 

 van Cassavemeel. Ind. Merc. 30. 10. 



1906, p. 734, Bl. 105, p. 316. 



Die Krauselkrankheit der Manioc. 

 Tropenpfl. June 1906, p. 145. 



Culture et traitement du manioc a 

 Java. Journ. d'Agr. trop. Dec. 

 1905, p. 366. 



Manioc cultivation. Lewis. "T.A.' 



Feb. 1906, p. 58. 

 Starch manufacture from Cassava. 



"T.A." Jan. 1906, p. 833. 



L'etude du manioc daus 1' Est African 

 allemand., Journ. d'Agr. trop. Jan. 



1907, p. 15. 



Zimmermann. Einige Bemerkungen 

 fiber Maniok. Der Pflanzer. 1906, 

 p. 257. 



