174 



some cases the causes for this distribution can be apprehended, 

 e. g. the leguminous plants are supplied with nitrogen from the 

 atmosphere and are therefore fully fed by a fertiliser containing 

 phosphates and potash but no nitrogen, a mixture which is of 

 little or no use to the grasses. Again, ammonium salts encourage 

 shallow rooting plants, because they are retained by the surface 

 layer of soil ; nitrate of soda is, on the contrary, washed down by 

 the rain and encourages deep, tap-rooting plants. Such expla- 

 nations do not, however, cover all the facts observed. In view of 

 the great divergencies in vegetation thus artificially induced it might 

 seem a simple problem to find out by the analysis of a particular 

 soil and plant how to adapt another soil to that plant: at once 

 however, there are difficulties. All plants contain the same ele- 

 mentary substances derived from the soil and in very much the 

 same sort of proportions. We can group plants into silica lovers, 

 lime lovers and potash lovers by the prominence of these parti- 

 cular constituents in their ash, but on experiment these groupings 

 possess little significance, because the differences betwen the com- 

 position of the same plant growing on different soils are often 

 greater than those separating the various groups. Soils of the most 

 diverse type possess much the same chemical composition. How, 

 then, reconcile these facts with the great differences in the nature 

 of the herbage of the Rothamsted plots which have been established 

 by differences in the chemical nature of the food supply? The 

 intense competition existing between the various species on these 

 plots must be taken into consideration; if the treatment, chemical 

 or otherwise, establishes only a small difference in favor of one 

 species as against another, then the pressure of competition acting 

 over a long period, may easily eliminate the one species or make 

 the other predominant. It thus becomes necessary to look for 

 very small factors and not expect any large special correlation of 

 the chemical composition of plant and soil. 



A. D. HALL. The Association of Plant and Soil. [Fourth 

 Masters Lecture]. The Gardeners' Chronicle, N. 3613, p. 206. 

 London, March 26, 1910. 



Delivering the second of the Masters Memorial lectures for 1910, 

 Mr A. D. Hall, Director of the Rothamsted Experimental Station, said 

 that in order to obtain some basis of knowledge for the associations 

 of given plants with certain soils, one must turn to farm crops, about 

 the requirements of which so much was known. A map had 



