THE PHYSIOLOGY OF COLOR IN PLANTS. 79 



end of the spectrum, which, as has been pointed out, is the one 

 which causes disintegration in the cells, as well as the lower red 

 and infra-red rays. The spectrum of the autumnal red coloring 

 of the leaves of the Virginia creeper {Ampelopsis) is shown in 

 Fig. 1, III. It may be safely asserted that the above-described 

 occurrences of coloring matter are undoubtedly marked factors 

 in the physiology of a large number of plants, without reference 

 to the manner in which such coloring screens and shields have 

 arisen. It is also true, however, that a large number of plants 

 contain coloring matters in the interior of organs or disposed in 

 such other manner that they could sustain no possible relation 

 either to light or to animals furnished with a color sense ; still, 

 many other occurrences of color are to be noted in which a physi- 

 ological function is quite possible but is not proved. Among 

 the latter is the color formation which ensues in evergreen leaves 

 on the approach of a cold season, or in other leaves on the ap- 

 proach of a dry season. It must be admitted that in some in- 

 stances physiologists have been led to conclusions concerning the 

 use of colors quite as little justified as many of those reached by 

 enthusiastic students of " adaptation to insect visitors." It is now 

 somewhat generally admitted that color substances must very 

 often be regarded as simply by-products in the chemical processes 

 carried on by plants ; a view which is undeniably valid of color 

 masses in the interior of underground roots or tubers, or massive 

 aerial organs, and also in a large number of instances in flowers. 

 This latter application is further justified hj the fact that some 

 flower colors may change during the season without any relation 

 to light conditions, insect visitors, or other ecologic factors. It is 

 quite within the range of possibility that color masses in aerial 

 organs bear an important modifying relation to the forms of 

 irritability to radiant energy acquired by the plant. 



As a summation of the foregoing, it may be stated that color- 

 ing matters stand in the following relations to the plants: 



1. Chlorophyll converts light into energy by the aid of which 

 protoplasm containing it is able to build up foods from carbon 

 dioxide and water. 



2. Non-green coloring substances serve as a screen between 

 the chlorophyll and the too violent rays of the sun, at the same 

 time converting the absorbed portion of the rays into useful heat. 



3. Non-green coloring substances convert the light which has 

 passed the chlorophyll bodies into useful heat. 



4. Coloring substances absorb the blue-violet rays and prevent 

 their disintegrating effect on nitrogenous compounds in situ or in 

 transit in the interior of the plant. 



5. Non-green coloring substances are in some instances simply 

 by-products or waste matter from the physiological processes, and 



