CO-OPERATION AND THE ORIGIN OF FLOWERS. 151 
were in all probability inconspicuous so as to escape the 
eyes of marauding insects. 
True flowers are conspicuously coloured to attract in- 
sects. Colour and scent are surely characteristic of our ideas 
of a flower. 
The first question is, then, how did the ancestors’ leaves 
become coloured? 
In almost all flowers a group of chemical substances 
called the anthocyans are responsible for colouring. Strong 
sunlight directly produces this material (anthocyan), as has 
been proved by many observations. 
Even in Scotland I have found that if Foxgloves are 
grown in dry, exposed, and sunny situations, which is, of 
course, not their natural habitat, their leaves and bracts tend 
tc become purplish red. 
In very dry exposed places, such as railway tracks, dry 
banks, rocks specially by the sea, many other plants show 
this anthocyanic reddening.* 
A large proportion of arctic and high alpine plants are 
also stated to show similar changes in colour of the foliage 
and stems. Many other observations could be quoted, but 
the following three may be sufficient. Becker in his mono- 
graph on Anthyllis remarks on the reddening of the calyx in 
sunny and drv climates?; Farmer finds that the leaves of 
Hydrocharis become red in sunlight; and Macfarlane found 
that the pitchers of Nepenthes were more richly coloured in 
sunny positions." 
So far as flowers are concerned, the effect of Alpine sun- 
shine is quite well known. Bonnier and others found that 
plants from high altitudes in the Alps lost much of their 
brilliancy when grown in the plains, and also that others 
taken from low altitudes and grown in gardens at great 
elevations became richer and deeper in colouring. Moreover, 
in these short Alpine meadows, there is an extraordinary pro- 
fusion of blossoms. On the Salampe Alp, at 1950 metres, 
where blizzards and snowstorms alternate with blistering 
* More detailed observations are required (third series). 
