PROCEEDINGS 



OF THE 



HORTICULTURAL SOCIETY OF LONDON, 



1843. 



No XXI. 



January '2, 1843. 

 GARDEN COMMITTEE. 

 The following reports were read. 



Hothouse Department. — Some experiments with Hydrangeas 

 have now produced results which enable me to communicate to 

 the committee the fact that alum disolved in water, or reduced 

 to powder and mixed with the soil, has the property of changing 

 the colour of the flowers from their natural pink to blue. Other 

 substances may possibly do so as well as alum, and therefore 

 without a careful analysis of those soils whicii are generally used 

 to produce the blue colour, it will be impossible to say whether 

 it is alum in them which produces the eflfect or not. It is however 

 more than probable that that is the cause. Oxide of iron is 

 generally supposed to produce the blue colour, but I have not 

 been able to detect the slightest tinge when that was used 3 on 

 the contrary I thought it produced a deeper red. 



I should add that the idea of applying alum did not originate 

 with me 3 that substance is recommended in several works on 

 gardening, but its effects seemed to want confirmation. 



R. Fortune, Superintendent. 



Hardy Department. — In the spring when the Armerias and 

 Statices commenced growing, some plants were watered with a 



