TOXIC ACTION OF ONE CROP ON ANOTHER 301 



grass becomes affected, in an alteration in its composition. In 

 the case of fruit trees, the effect of shading is probably insignifi- 

 cant. It was noticed in one instance where Brussels sprouts 

 had been grown in a mixed plantation, that, although the crops 

 under the trees had been very much affected, there was no 

 difference observable between the more shaded and less shaded 

 positions. A definite experiment on the subject emphasised this 

 point. A piece of ground occupied irregularly with fruit trees 

 mostly standard apples up to 23 years of age was planted 

 with sprouts : in the rest of the ground plots similar in size and 

 number to the spaces occupied by the trees, were marked off, 

 and shaded by canvas screens five feet above the ground, which 

 certainly shaded the plants more than did the trees : at the same 

 time, other plots were marked off where trees had been growing 

 until the sprouts were planted, these trees having been cut down, 

 without disturbing the subsoil, for the purpose of the experiment. 

 The results obtained in two successive years gave the following 

 values for the relative crops from the different plots 



Unoccupied ground ..... 100 



Under trees ...... 62 



Under screens . . . . . 101 



On former tree-sites ..... 100 



Thus, the effect of the trees was to reduce the vigour of the 

 plants by 38 per cent., but this reduction could not be attributed 

 to shading, for the still greater shading produced by the screens 

 had caused no reduction at all; nor was it due to the ground 

 having become exhausted by the trees, for no similar reduction 

 had occurred where the sprouts occupied former tree-sites. 



Practical l men have long ago made up their minds that plants 

 do have a very great effect on the soil in which they are growing. 

 But the old idea, handed down from mediaeval times, and taught 

 in the best text-books of the eighteenth century, was that the 

 soil was the source of life and food for the plant, and that the plant 

 played simply a passive part, accepting whatever the soil sup- 

 plied to it. When, however, modern scientific investigation began, 

 it was discovered that the plant was by no means a merely pas- 

 sive agent, but that it got much of its sustenance from the air, 

 and that even such sustenance as it derived from the soil, was 

 not 'really food in the proper sense of the word, but only the raw 



1 The following seven paragraphs form an abridgment of an article on 

 the subject written by E. J. Russell for the XlVth Woburn Report, p. 51. 



