16 R. A. EMERSON 
environmental diversities. A prominent geneticist, on observing some 
of the writer’s cultures, was led to say that there were no sharply differ- 
entiating characteristics by which other than an arbitrary classification 
could be made, and asserted that he could select from a single progeny a 
series grading from the darkest to the lightest colors. The writer has 
some doubt that this could have been done, but the instance illustrates 
well the difficulties that confront one unacquainted with the materials. 
It is fortunate thaé some environmenta! influences which increase the 
difficulty of assorting certain color types make other types stand out more 
sharply than they otherwise would. Without some notion of these envi- 
ronmental effects, a genetic analysis of the material would indeed be 
difficult. 
SUNLIGHT A FACTOR IN COLOR DEVELOPMENT 
The relation of sunlight to the development of color has been noted 
briefly in the descriptions of some of the color types. The effects of 
sunlight or of local darkness, instead of adding to the confusion of color 
types, afford a means of sharp differentiation between certain types. 
So far as is known at present, no color develops in sun red or dilute sun 
red plants, or in the early stages of growth of dilute purple plants, except 
under the influence of fairly strong light. In the case of purple and of 
the later stages of growth of dilute purple, there is no doubt that the 
color develops more rapidly at first in light than in darkness, but ulti- 
mately color develops fully, or apparently so, even in local darkness 
(Plate VIII). The seedlings of purple plants develop some color when 
germinated and grown in a dark chamber where no part of the plant receives 
light. There is some, tho very little, evidence that the development of 
brown pigment of type V is hastened by the influence of light, and what 
little brown color ever develops in type Vla is confined to parts exposed 
to sunlight (Plate VI, 5). 
It would not be surprising to find that the pigments seen in the purple, 
dilute purple, sun red, and dilute sun red types are the same chemically. 
In fact they look alike in water solution and apparently react in the same 
way to simple chemical tests. If they prove to be identical, it would seem 
to follow that purple and dilute purple plants have some inherent 
mechanism, perhaps an organic catalyzer, capable of initiating or hasten- 
ing chemical reactions, and that this mechanism is lacking in sun red 
