78 DOMESTICATED ANIMALS AND PLANTS 
and animals, and it is worth the while to note briefly how nature 
produces such marvelous effects in such natural ways.! 
Colors of animals and plants are due to the following distinctly 
different causes : 
1. The manufacture of specific coloring materials or pigments 
either as a necessary part of the body activities or as a matter 
of accident. For example, the universal green color of plants is 
due to chlorophyll, the blue of which fades as the leaf ages or 
yields to the influence of cold, leaving the yellow behind to char- 
acterize the foliage of autumn.? The green of birds is due to 
a specific pigment with no physiological function like that of 
chlorophyll ; it is a color never found in mammals. 
Red, on the other hand, is widely diffused among both plants 
and animals. The red color of blood is due always to hamo- 
globin, a substance also produced by a great variety of organisms. 
Red pigments, however, are produced by plants, especially in the 
flowering parts and in the leaves of certain species, rarely during 
the growing period, but more commonly late in the season. 
Yellow, whether in plant or animal, is the result of an oily 
pigment, and the three pigments, yellow, blue, and red, in vary- 
ing proportions and distribution are capable of producing about 
every color found in nature, though browns, blacks, and even 
occasionally whites are the result of specific pigment.? 
1 We have a habit of mind which leads us to feel that when an event or 
occurrence is known to be natural, then all mystery is cleared away. This 
attitude of mind is wrong, and it deprives us of some of our chief opportunities 
for higher meditation. We plant a seed and it grows into a tree. We say, 
“There is no mystery in that,— it was natural”; but the truth is that if we really 
consider all that has happened, we shall see that a greater miracle has been 
performed than the making of the dumb to speak, the blind to see, or even the 
raising of a man from the dead. With all of our philosophy and all of our 
science we know nothing about life, — whence it comes or how it works; we 
only know some of the things it does. 
? The student is reminded that green is not a primary color, but a mixture 
of yellow and blue. 
* The student will remember that the so-called three-color process of print- 
ing succeeds in reproducing practically all colors by the proper mingling of 
these three primaries — red, yellow, and blue. Nature does the same. 
