ON THE COLOURS OF SPRING FLOWERS. 315 
grandiflora , Franthis hy emails, Forsythia viridissima, Tussilago 
Farfara. 
It is worth noting that these are without exception early, 
and some of them very early, spring-flowering plants. The 
colours, therefore, which pre-eminently distinguish our summer 
and autumn flora, the reds, pinks, blues, and some yellows (not 
due to xanthine, hut to a soluble yellow pigment), are caused 
by the presence of substances which require both a strong light 
and a high temperature for their production, and Professor 
Batalin has shown this to be especially the case with the red 
colouring substance.* That the same species of flower fre- 
quently assumes a more intense colour with increasing altitude 
in the Alps is a matter of ordinary notice, confirmed by the 
exact observations of M. Bonnier, f who states that this change 
is due to an actual increase in the amount of colouring matter 
in the cells. The difference already pointed out between the 
prevailing colours of the spring flora in England and in Switzer- 
land, seems to me to be due to the same cause. Owing partly 
to the spring being a month later, partly to the more southern 
latitude, and consequent greater elevation of the sun, partly to 
the clearer air of a high altitude, the light which opens the 
earliest spring flowers is much stronger in Switzerland than in 
England, causing the appearance of those brilliant roses and 
pinks of the Silenes, Ericas, and Primulas, and blues of the 
Gentianas, Soldanellas, and Phyteumas, with which we have, with 
the exception of our blue-bells, scarcely anything to compare in 
our spring flora. In the list given above, the most striking 
feature of the early spring flora of Switzerland is seen to be the 
very large ingredient of red and pink : but I believe a more 
complete analysis would show an almost equal preponderance of 
blue. 
I have not in this paper touched on the interesting subject 
of the adaptation of the various colours of flowers to fertilization 
by insect agency, about which much has been, and very much 
might be, written. As Hermann Muller points out in his most 
recent publication, J changes in the colour or form of flowers 
which are serviceable to them for purposes of fertilization, can 
only be the result of external physical causes, and must be 
perpetuated by natural selection acting on heredity. This 
writer, who has made the subject specially his own, fully 
confirms the statement of the greater brightness of colour of 
the flora of the Alps as compared with that of the plains, a 
result not only of the occurrence of brighter-flowered species, 
* Acta liort. Petr op. VI. ii. p. 279. 
t Bull. Soc. Bot. France , xxvii. (1880), p. 103. 
X Alpenblumen ; Hire Befruchtung durch InseJcten und Hire Anpassungen 
an dieselben. Leipzig , 1881. 
