628 



SCIENCE 



[N. S. Vol. XXVIII. No. 723 



growth can not profitably be renewed until 

 an interval of some years has elapsed. 



Again it is well known that when a plant 

 is sown upon land which has not carried 

 that particular crop for many years be- 

 forehand it starts into growth with a 

 vigor it rarely displays upon land where it 

 forms an item in the regular rotation, even 

 though the new land is so impoverished 

 that the final yield is indifferent. In the 

 instance quoted above, where swedes were 

 sown on Little Hoos field, Rothamsted, 

 after a very long interval, although the 

 yield was poor on the unmanured plots, yet 

 the seeds germinated and made their early 

 growth in a very remarkable fashion, in- 

 comparably better than did the same seed 

 sown upon adjoining land in a high state 

 of fertility, but which had been cropped 

 with swedes from time to time previously. 

 There is thus 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 which unfits it for the 

 renewed growth of the crop. The injuri- 

 ous action may even arise from the growth 

 of a different crop, as in the well-known 

 experiments at the Woburn Fruit Farm, 

 where Pickering has shown that the roots 

 of grasses exert a positively injurious 

 effect, distinct from competition for food, 

 water or air, upon fruit trees growing in 

 the same soil. 



Assuming that the persistence in the soil 

 of obscure diseases appropriate to the par- 

 ticular plant can be neglected as the cause 

 of these phenomena, there still remains 

 some unexplained factor arising from a 

 plant's growth which is injurious to a suc- 

 ceeding crop, and this may either be 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 microflora accumulating 

 in the particular soil layer in which the 

 roots of the crop chiefly reside. 



Experimental evidence is as yet wanting 

 as to these highly complex interactions be- 

 tween the higher plants and the microflora 

 of the soil, but Russell and other observers 

 have shown how greatly a disturbance of 

 the normal equilibrium of the flora of the 

 soil may affect its fertility, as measured by 

 the yield of a higher plant. Partial steril- 

 ization, such as is brought about by heat- 

 ing the soil to 98° for ten hours, wiU 

 double the yield of the succeeding crop 

 and will show a perceptible beneficial effect 

 up to the fourth crop after the heating, 

 and exposure to the vapors of volatile anti- 

 septics like toluene or carbon bisulphide, 

 which are afterwards entirely removed by 

 exposure, will increase the yield in a simi- 

 lar but smaller degree ; even drying the soil 

 appears to have an influence upon its 

 fertility. 



It is in this direction, perhaps, that the 

 clue may be found to the unexplained 

 benefits of the rotation of crops, and to 

 some of the other facts difficult of explana- 

 tion upon the ordinary theories of plant 

 nutrition, which have been advanced by 

 Whitney and his co-workers. The soil, 

 however, is such a complex medium — the 

 seat of so many and diverse interactions, 

 chemical, physical and biological— and is 

 so unsusceptible of synthetic reproduction 

 from known materials, that experimental 

 work of a crucial character becomes ex- 

 tremely difficult and above all requires to 

 be interpreted with extreme caution and 

 conservatism. A. D. Hall 



Rothamsted Experiment Station 



THE DUBLIN MEETING OF THE BRITISH 

 ASSOCIATION— II. 



The Metabolism of the Plant Considered 

 as a Catalytic Reaction'^ 



Aptee outlining the three fundamental 

 principles of reaction-velocity, the law of 



' Address by Professor F. F. Blackman, M.A., 

 F.R.S., president of the botanical section, on " The 

 Manifestations of the Principles of Chemical 

 Mechanics in the Livini; Plant." 



