TRANSACTIONS OF SUB-SECTION B— CHAIRMAN'S ADDRESS. 571 



SUB-SECTION OF AGRICULTURE. 

 Chairman. A. D. Hall, M.A., F.R.S. 



THURSDAY, SEPTEMBER 1. 



The Chairman delivered the following Address : — 



1 believe it is customary for anyone who has the honour of presiding over a 

 section of the British Association to provide in his presidential address either a 

 review of the current progress of his subject or an account of some large piece 

 of investigation by which he himself has illuminated it. I wish I had 

 anything of the latter kind which I could consider worthy to occupy your atten- 

 tion for the time at my disposal; and as to a review of the subject, I am not 

 without hopes that the sectional meetings themselves will provide all that is 

 necessary in the way of a general review of what is going forward in our depart- 

 ment of science. I have, therefore, chosen instead to deal from an historic point 

 of view with the opinions which have prevailed about one central fact, and I pro- 

 pose to set before you this morning an account of the ebb and flow of ideas as to 

 the causes of the fertility of the soil, a question which has naturally occupied the 

 attention of everyone 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 cultivation, 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 century, which we may take as the beginning 

 of organised 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 

 experiment we have recorded is that of Van Helmont, who placed 200 lb. of dried 

 earth in a tub, and planted therein a willow 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 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 obtaining similar results, except 

 when his gardener lost the figures, an experience that has been repeated. Boyle 

 also distilled his pumpkins, &c, and obtained therefrom various tars and oils, 

 charcoal and ash, from wnich 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 growing 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 lacking. Some instinct seems to have led them to regard 

 nitre 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 Philo- 

 sophical Knowledge by Experiment, in a lecture on the vegetation of plants, 

 describes an experiment in which he watered young barley plants with a weak 

 solution of nitre and found that their growth was promoted thereby ; and John 

 Mayow, that brilliant Oxford man whose early death cost so much to the young 

 science of chemistry, went even further, for, after discussing the growth of nitre 

 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 



