THE ADAPTATION OF THE PLANT TO THE SOIL. 



21 



A direct example of that may be seen at Eotliamsted ; in the year 

 1888 a portion of the wheat field was not hai^ested but left to reproduce 

 itself naturally. A good crop came up in the following year from the 

 self-sown seed, but throve very badly in the competition that ensued 

 with the weeds. After four years only a few dozen starved ears of 

 wheat could be found over the whole area, and since that time the 

 wheat has entirely disappeared, and the land is occupied by intrusive 

 grass and weeds of all kinds. Here, then, we see that wheat, which 

 has been educated to yield a great bulk of material, may yet become 

 incapable with all its vigour of competing with the plants which we 

 typically call weeds, when both are left to struggle on the same piece 

 of ground. Thus it will be seen that the experimental study of the 

 association of particular plants with particular soils is fraught with 

 difficulties of interpretation, so easily do secondary factors come into 

 play and obscure the point at issue. 



It has been my object in these lectures thus to point out the main 

 factors which determine some causal connection between plant and 

 soil. There are certain special cases where the presence of particular 

 constituents in the soil, e.g. zinc, seems to produce pathological dis- 

 turbances in the plant to the extent of giving rise to something which 

 almost appears to be a new species. We have even met with reports 

 indicating the possibility of thus bringing about those teratological 

 changes which were studied by the distinguished man in whose honour 

 these lectures were founded. The evidence is still too scrappy to be 

 worth theorizing about ; it is experiment that is called for in all 

 these directions. The object of my lectures has been more to indicate 

 the existence of these problems and the state of our ignorance than 

 to provide you with any consistent theory or body oi information. 

 Obviously there cannot be a complete science of horticulture until we 

 have ascertained both the most fitting soils in which tO' grow our garden 

 plants and the reasons that underlie the choice, but it is by experiment 

 and by experiment alone that such knowledge will be attained. 



[Note. — Figures 1-7 are reproduced from the author's Book of the Rothamsted 

 Experiments, and figs. 8-11 from the Journal of the Farmers'' Club, by kind 

 permission of Mr. John Murray and the Farmers' Club respectively.] 



