r 201 ] 



No. 23. 



THE HYDROGEN ION CONCENTRATION OP THE SOIL IN RELATION 

 TO THE FLOWER COLOUR OP HYDRANGEA H0RTEN8IS W., 

 AND THE AVAILABILITY OP IRON. 



By W. R. G. ATKINS, O.B.E., Sc.D., P.I.C. 



(Read March 27. Printed June IS, 1923.) 



Floiuer Colour and Soil Reaction. 



When studying the relation between the distribution of plants and the 

 hydrogen ion concentration of the soil (Atkins, 1922, 1), it was noticed that pink 

 hydrangeas were found on alkaline soil and blue on acid. A number of 

 situations were examined to test the validity of this observation ; the results are 

 given in the following table : — 



There is in these examples undoubted proof of the relation between soil 

 reaction and flower colour. They include the case of a plant originally bearing 

 blue flowers changing to pink when in an alkaline habitat, as at Cornwood, and 

 the converse change, pink to blue and some pinkish, at Templemicbael. 



Some plants bear blue and pink flowers; these are found in situations with 

 a reaction of pH 75 and under. It must be added that the soil tested was from 



SCIENT. PROC. R.D.S., VOL. XVII, NO. 23. 2 O 



