66 COLORS OF VEGETATION. 
family the blue substance should be found to predominate, and in 
the yellowish-green leaves of the hickories the yellow substance 
should be in the ascendant. Indeed it has been found that, in the 
outer leaves of the cabbage, the phyllocyanin or blue substance 
exists in much greater proportion than in the inner leaves which 
have been deprived of sunlight. 
Now as to the physical causes producing differences of inten- 
sity. In the dark shining leaves such as those of the laurel, 
prince’s pine, partridge berry, etc., the depth of color is due to 
the closeness with which the cells are packed together. Each cell 
contains a globule of chlorophyl, and it is evident that, other 
things being equal, the smaller the cells and the more compact 
their arrangement, the darker will be the color of the leaf. 
And as to the differences in vividness of color. In the young 
leaves of the horse-chestnut, the cuticle is very thin and the cellu- 
ar substance of the leaf is very transparent; hence the green of 
the globules of chlorophyl shows brightly through. On the con- 
trary, in the Cassandra or leather leaf, the cellular tissue is of a 
thick husk-like texture and the leaves are of necessity dull colored. 
The blue coloring substance in leaves is much less stable than 
the yellow. It rapidly decomposes or is transformed in the 
absence of sunlight. You have all noticed what a yellow hve the 
foliage of trees wears in wet and cloudy springs, and even in 
summer, a week or two of sunless weather will often make a 
perceptible differenge in the color of the woods. Always the 
lower and inmost leaves of a tree are paler than the rest and of a 
yellowish hue, like the complexion of boys “brought up in the 
house.” Cold weather bleaches chlorophyl and vegetable coloring 
matters generally. The further north we go the more liable do 
we find plants to albinism or loss of color. Flowers of Arctic or 
mountainous regions are always paler and more delicate in hue 
than those of warm countries and they are far more subject to 
white varieties. Linnzus’ says that ‘‘ there is not a single blue or 
red flower in Lapland that has not its white varieties.” The yel- 
low coloring matter is much less easily affected by absence of light 
and other causes and yellow flowers rarely exhibit any striking 
ce eae in hue. Many plants are entirely destitute of chloro- 
: are parasites, and as they depend for their nutrition 
- si m already elaborated by the supporting plant they have 
eles: me ernst The cells may be filled with orange-purple 
