Wakeman—Pigments of Flowering Plants. 
767 
PIGMENTS OF FLOWERING PLANTS. 
By Nellie A. Wakeman. 
INTRODUCTORY CHAPTER. 
Theories of Color in Organic Compounds. 
While the study of pigmentation in plants early attracted the 
attention of chemists as well as botanists, it was not until the in¬ 
troduction of synthetic dye stuffs in the latter part of the 19th 
century that any considerable amount of attention was directed 
to the determination of the cause of color in the pigment itself. 
Until this time indeed, the constitution of most of the na¬ 
tural dye stuffs was unknown, consequently any consideration 
of the relationship between color and molecular structure was 
impossible. With the introduction of dye stuffs of known 
constitution, however, the question not only presented itself 
but well nigh forced itself upon the attention of chemists. The 
earlier endeavors were, for the most part, directed toward de¬ 
termining a direct relationship between color and molecular 
constitution. This led to a study of so-called chromophorous 
groups and chromogens, a study which, while it has been fruit¬ 
ful of results in the manufacture of dye stuffs, has been of 
much less value in the study of plant pigments. Recently, 
however, these studies have assumed a more basal character 
and the subject has been approached through the general ques¬ 
tion of absorption spectra, the invisible as well as the visible 
portion of the spectrum being taken into consideration. 
It is obvious that color does not inhere in the colored sub¬ 
stance itself, but is the response of sensation to the stimulus of 
light which proceeds from the colored substance either by trans¬ 
mission or reflection. The different dyes and pigments pos¬ 
sess their many varying hues because, by a process known as 
