364 



SCIENCE 



[N. S. Vol. XXXII. No. 820 



of every one who has exercised his reason 

 upon matters connected with agriculture. 

 The fertility of the soil is perhaps a vague 

 title, but by it I intend to signify the 

 greater or less power which a piece of land 

 possesses of producing crops under culti- 

 vation, or, again, the causes which make 

 one piece of land yield large crops when 

 another piece alongside only yields small 

 ones, differences which are so real that 

 a farmer will pay three or even four 

 pounds an acre rent for some land, whereas 

 he will regard other as dear at ten shillings 

 an acre. 



If we go back to the seventeenth cen- 

 tury, which we may take as the beginning 

 of organized science, we shall find that 

 men were concerned with two aspects of 

 the question — how the plant itself gains 

 its increase in size, and, secondly, what the 

 soil does towards supplying the material 

 constituting the plant. The first experi- 

 ment we have recorded is that of Van 

 Helmont, who placed 200 lb. of dried 

 earth in a tub, and planted therein a wil- 

 low tree weighing 5 lb. After five years 

 the willow tree weighed 169 lb. 3 oz., 

 whereas the soil when redried had lost but 

 2 oz., though the surface had been care- 

 fully protected meantime with a cover of 

 tin. Van Helmont concluded that he 

 had demonstrated a transformation of 

 water into the material of the tree. 

 Boyle repeated these experiments, growing 

 pumpkins and cucumbers in weighed earth 

 and obtaining similar results, except when 

 his gardener lost the figures, an experience 

 that has been repeated. Boyle also dis- 

 tilled his pumpkins, etc., and obtained 

 therefrom various tars and oils, charcoal 

 and ash, from which he concluded that a 

 real transmutation had been effected, 

 "that salt, spirit, earth, and even oil 

 (though that be thought of all bodies the 



most opposite to water) may be produced 

 out" of water. ' ' 



There were not, however, wanting among 

 Boyle's contemporaries men who pointed 

 out that spring water used for the grow- 

 ing plants in these experiments contained 

 abundance of dissolved material, but in the 

 then state of chemistry the discussion as 

 to the origin of the carbonaceous material 

 in the plant could only be verbal. Boyle 

 himself does not appear to have given any 

 consideration to the part played by the soil 

 in the nutrition of plants, but among his 

 contemporaries experiment was not lack- 

 ing. Some instinct seems to have led them 

 to regard niter as one of the sources of 

 fertility, and we find that Sir Kenelm 

 Digby, at Gresham College in 1660, at a 

 meeting of the Society for Promoting Phil- 

 osophical Knowledge by Experiment, in a 

 lecture on the vegetation of plants, de- 

 scribes an experiment in which he watered 

 young barley plants with a weak solution 

 of niter and found how their growth was 

 promoted thereby; and John Mayow, that 

 brilliant Oxford man whose early death 

 cost so much to the young science of chem- 

 istry, went even further, for, after discus- 

 sing the growth of niter in soils, he pointed 

 out that it must be this salt which feeds 

 the plant, because none is to be extracted 

 from soils in which plants are growing. 

 So general has this association of niter 

 with the fertility of soils become that in 

 1675 John Evelyn writes: "I firmly be- 

 lieve that where saltpeter can be obtained 

 in plenty we should not need to fijid other 

 composts to ameliorate our ground"; and 

 Henshaw, of University College, one of 

 the first members of the Eoyal Society, also 

 writes about saltpeter: "I am convinced 

 indeed that the salt which is found in veg- 

 etables and animals is but the niter which 

 is so universally diffused through all the 

 elements (and must therefore make the 



