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but also of tbe greater intensity of colour in the same species. 
This he attributes to the greater transparency of the mountain 
air, and consequent more intense light, an explanation which is 
confirmed by the experiments of Siemens with the electric 
light.* The observations of Muller with regard to the pre- 
valent colours of Alpine flowers are completely in accord with 
those stated above, viz., the comparative scarcity of white, and 
the remarkable prevalence of red and blue flowers ; he further 
states that those flowers only are red or blue which are visited 
chiefly or exclusively by bees and ‘ hover-flies 9 (Syrphidae). 
It would be interesting to compare this fact with the time of 
year at which these groups of insects are most abundant. 
The conclusions arrived at in this paper are somewhat at 
variance with those of Mr. Buchan, f who states that the blues, 
on the average, flower considerably the earliest ; then, in order, 
the whites, purples, and, lastly, the yellows and reds. It is 
possible that the discrepancy may arise from Mr. Buchan 
having based his result on the entire English flora, while I 
have taken only the commonest flowers. 
* See Nature , 1880, vol. xxi. No. 535. 
t Proceedings of Edinburgh Botanical Society , 1876. 
