THE FERTILITY OF THE SOIL 5 



surface had been carefully 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 ob- 

 taining similar results (except when his gardener lost 

 the figures). BOYLE also distilled his pumpkins and 

 cucumbers, obtaining 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 the spring 

 water used for the growing plants in these experiments 

 contained abundance of dissolved material, but at that 

 time the discussion as to the origin of the carbonaceous 

 material in the plant could only be a matter of idle 

 words. BOYLE himself does not appear to have given 

 any consideration to the part played by the soil in the 

 nutrition of plants, but some of his contemporaries 

 carried out important experiments. Some instinct 

 seems to have led them to regard nitre as one of the 

 sources of fertility, and we find SIR KENELM DIGBY, 

 at Gresham College, in 1660, at the meeting of the 

 Society for Promoting Philosophical Knowledge by Ex- 

 periment, in a lecture on the vegetation of plants describes 

 an experiment in which he watered young barley with 

 a weak solution of nitre and found how its growth 

 was promoted thereby. JOHN MAYOW, that brilliant 

 Oxford man through whose early death the young 

 science of chemistry lost so much, went even further ; 

 for after discussing the presence of nitre in soils he 



