September 1G, 1910] 



SCIENCE 



365 



chief ingredient in their nutriment, and 

 by consequence all their generation), a lit- 

 tle altered from its first complexion." 



But these promising beginnings of the 

 theory of plant nutrition came to no 

 fruition; the Oxford movement in the 

 seventeenth century was but the false 

 dawn of science. At its close the human 

 mind, which had looked out of doors for 

 some relief from the fierce religious con- 

 troversy with which it had been so long 

 engrossed, turned indoors again and went 

 to sleep for another century. Mayow's 

 work was forgotten, and it was not until 

 Priestly and Lavoisier, De Saussure, and 

 others, about the beginning of the nine- 

 teenth century, arrived at a sound idea of 

 what the air is and does that it became 

 possible to build afresh a sound theory of 

 the nutrition of the plant. At this time 

 the attention of those who thought about 

 the soil was chiefly fixed upon the humus. 

 It was obvious that any rich soils, such as 

 old gardens and the valuable alluvial 

 lands, contained large quantities of or- 

 ganic matter, and it became somewhat 

 natural to associate the excellence of these 

 fat, unctuous soils with the organic matter 

 they contained. It was recognized that the 

 main part of a plant consisted of carbon, 

 so that the deduction seemed obvious that 

 the soils rich in carbon yielded those fatty, 

 oily substances which we now call humus 

 to the plant, and that their richness de- 

 pended upon how much of such material 

 they had at their disposal. But by about 

 1840 it had been definitely settled what the 

 plant is composed of and whence it derives 

 its nutriment — the carbon compounds 

 which constitute nine tenths of the dry 

 weight from the air, the nitrogen, and the 

 ash from the soil. Little as he had con- 

 tributed to the discovery, Liebig's brilliant 

 expositions and the weight of his authority 

 had driven this broad theoiy of plant nu- 



trition home to men's minds; a science of 

 agricultural chemistry had been founded, 

 and such questions as the function of the 

 soil with regard to the plant could be 

 studied with some prospect of success. By 

 this time also methods of analysis had been 

 so far improved that some quantitative 

 idea could be obtained as to what is pres- 

 ent in soil and plant, and, naturally 

 enough, the first theory to be framed was 

 that the soil's fertility was determined by 

 its content of those materials which are 

 taken from it by the crop. As the supply 

 of air from which the plant derives its 

 carbonaceous substance is unlimited, the 

 extent of growth would seem to depend 

 upon the supply available of the other 

 constituents which have to be provided by 

 the soil. It was Daubeny, professor of 

 botany and rural economy at Oxford, and 

 the real founder of a science of agricul- 

 ture in this country, who first pointed out 

 the enormous difference between the 

 amount of plant food in the soil and that 

 taken out by the crop. In a paper pub- 

 lished in the Philosophical Transactions 

 in 1845, being the Bakerian Lecture for 

 that year, Daubeny described a long series 

 of experiments that he had carried out in 

 the botanic garden, wherein he cultivated 

 various plants, some grown continuously 

 on the same plot and others in a rotation. 

 Afterwards he compared the amount of 

 plant food removed by the crops with that 

 remaining in the soil. Daubeny obtained 

 the results with which we are now familiar, 

 that any normal soil contains the material 

 for from fifty to a hundred field crops. 

 If, then, the growth of the plant depends 

 upon the amount of this material it can 

 get from the soil, why is that growth so 

 limited, and whj- should it be increased by 

 the supply of manure, which only adds a 

 trifle to the vast stores ">f piant food al- 

 readj' in the soil? For eiampie, a turnip 



