314 
POPULAR SCIENCE REVIEW. 
Out of fifty species in this list (one Androsace chamcejasme , 
being again reckoned twice over among the whites and pinks), 
18, or 36 per cent are white ; 1, or 2 per cent green ; 10, or 20 
per cent red or pink ; and 8, or 16 per cent blue or violet. 
Several points of contrast between these two lists will at 
once suggest themselves. The very small number of green 
flowers in the second may no doubt be due partly to the fact 
that Seboth’s work includes a selection only of Alpine flowers 
suitable for cultivation. But this will hardly account for the 
other differences ; the smaller proportion of white flowers, and 
especially the very much larger proportion — about three and a 
half times as many — of red and pink flowers, a fact which will 
be in accordance with every one’s recollection of the early 
spring flora of Switzerland. Now let us see whether we can 
arrive at any general conclusions from these data. 
In the first place, it must be borne in mind that the two 
colours white and green stand on a different footing from all 
the rest, and may be regarded as, more correctly speaking, an 
indication of the absence of colour. The colour of green petals 
is not due to a mixture of blue and yellow pigments, but to the 
presence of chlorophyll, the ordinary green colouring matter of 
leaves. The bright colours of petals are not usually assumed 
till immediately before their emergence from the bud ; and not 
a few — as for example those of Cobcea scandens, are still green 
when they first open, acquiring their proper colour only on full 
exposure to the light and warmth. A white flower again does 
not owe its colour to a milk-white fluid in the cells of the petals, 
but to the presence of air. Seeing, therefore, that the bright- 
coloured fluid pigments of petals are formed only under the 
influence of a sufficient supply of light and heat, the large pro- 
portion of green and white in our early spring flowers is easily 
accounted for. Then with regard to yellow, I find an exceed- 
ingly interesting observation by M. Flahaut* that ‘ a solid 
insoluble pigment, the xanthine of Fremy and Cloez, is in the first 
place to be distinguished from all the soluble colouring matters, 
blue, yellow, red, and their mixtures, all of which are acted on 
very readily by reagents, and which are usually formed only in 
the epidermal cells.’ This xanthine Fremy states to occur 
always in ‘ the form of clearly defined grains, occasionally in 
the epidermal, much more often in the deeper-lying cells, 
slowly soluble in alcohol and potassa. It is in all probability a 
modification of chlorophyll.’ The following is a list of the 
plants in which he has detected it : — Ranunculus, Primula, 
Cheiranthus , Galeobdolon luteum, JDoronicum plantagineum, Alys- 
sum saxatile, Cypripedium Calceolus, Azalea chinensis, Uvularia 
Bull. Soc. Bot. France , xxvi. (1879), p. 249. 
