COLORS OF VEGETATION. 67 
or tawny coloring substances or they may be empty, leaving a 
white plant, like the Monotropa and mushroom. Lichens and 
fungi growing on living or decaying organisms have also no need 
of chlorophyl; hence in the economy of nature they are unpro- 
vided with it. They often exhibit bright tints due to the presence 
of various coloring matters whose character is not well under- 
stood. Recent experimenters have succeeded in isolating some 
‘forty different coloring substances in a species of mushroom. 
Some fungi are luminous like the glow-worm. I do not know the 
theory of this. That peculiar luminosity of rotten wood, often 
supposed to be “ phosphorescence” and known by woodsmen as 
“ fox fire,” is due to the presence of a species of fungus. 
Much has been written about autumn coloration, but the subject 
has been treated from an esthetic rather than from a scientific 
standpoint. We are more interested in “the rosy cheek than we 
are to know what particular diet the maiden fed on.” However, 
in a general way, we say that the bright colors of leaves in the 
fall are caused by the oxidation of the chlorophyl. This is really a 
process of ripening. A brilliant autumn leaf is not dead but 
mature. ‘* Flowers are but colored leaves, fruits are but ripe ones. 
The edible part of most fruits is the parenchyma or fleshy tissue 
of the leaf of which they are composed.” The ripening of a 
maple leaf and a red astrachan apple is precisely the same process. 
In both cases it is an absorption of oxygen and a change of the 
blue substance of the chlorophyl to red. The yellow substance 
is not easily acted upon, hence the prevailing color of autumn 
foliage is scarlet, which is a mixture of yellow and red. 
M. Chatin has a different theory as to the production of scarlet 
leaves. He claims that the entire mass of chlorophyl is oxidized 
first to yellow and then to red, and that red leaves contain yellow 
chloropbyl in the inner cells which has not yet been oxidized. He 
thinks that yellow leaves in autumn are those in which the process 
has been arrested at the yellow stage before they arrive at red- — 
ness. But the leaves of the oaks become crimson without passing 
through any intermediate stages of yellow or scarlet. This theory 
also appears improbable in the case of the hickory, aspen, ete., 
whose bright yellow autumn foliage shows no tinge of red. Be- 
sides such a change as he imagines would be inconsistent with 
the theory of the compound nature of chlorophyl. 7 
It seems to be pretty well established by the experiments of 
