42 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



CHANGES OF COLOUR AND STRUCTURE OF FLOWERS 

 BY REMOVING SUNLIGHT AT SELECTED HOURS.* 



By Col. H. E. Rawson, C.B., R.E. (ret.). 



[Read March 2, 1915 ; Dr. F. Keeble, F.R.S., in the Chair.] 



It is owing to Dr. Fothergill's method of pressing flowers in such a 

 way as to retain the colours, that I am able to show you for the first 

 time, not photographs, but the actual flowers whose colours have been 

 changed by removing full sun from the plants at selected hours of the 

 day, while interfering as little as possible with the diffuse light at any 

 hour. The way this has been done artificially is described in the Reports 

 of the British Association for 1908 and 1913 ; but such screening can 

 be observed every day, by the posts and shelving of conservatories, the 

 walls of open gardens, and by natural woods, hills, hedges, and rocks. 

 Any opaque screen has proved to be sufficient, and whether it is set at 

 an angle overhead or placed vertically between the sun and the plant, 

 it need never interfere with the rainfall or the diffuse light. These 

 experiments have extended over the last nine years, and I much regret 

 that Dr. Fothergill's flower-presses were not perfected earlier, when I 

 should have been able to. show you all the changes of colour and 

 structure effected by the action of sunlight, from the time they first 

 occurred ; for, as you will see, the flowers can be mounted on cardboard 

 so as to appear as if they had just been picked, and dates and notes can 

 be added on the margin. I have tried painting the flowers, and even 

 doing so with their own pigments, photographing them in colours, and 

 preserving them in sand ; but the results have been open to suspicion 

 and unsatisfactory. I cannot express too highly my appreciation of 

 Dr. Fothergill's process, and even where much skill is required to 

 retain the exact hues of a red flower, for instance, this very fact is of 

 scientific interest. 



While I am not able to show you all the various stages, as they 

 arose, of such a change as from yellow to purple or from orange to 

 chocolate, I can show you the flowers as they now appear in an open 

 garden. Here is a series of twelve of each kind. They are those of 

 Tropaeolutn majus, the common garden Nasturtium, and the purple 

 variety was obtained from the ordinary orange and scarlet varieties, 

 twelve of which were growing in a clump in a garden at Pretoria, and 

 were all changed, with one exception, in less than three years, by a 

 South African sun, screened by one of the walls of the house and a belt 

 of trees over 100 feet away. Their seeds and that of the one exception 

 were brought to England and treated as nearly as possible in the same 



* The lecture was illustrated by specimens. 



