PIGMENTS 121 



identical external conditions of sunlight, moisture supply, etc. 

 The hereditary influence must completely overshadow the appar- 

 ent normal self -adjustment of pigment to energy-absorbing needs, 

 in all such cases. 



Again, it appears that there is some definite connection 

 between pigment content and respiration. It is known, of course, 

 that the gaseous exchanges involved in animal respiration are 

 accomplished through the reversible change of haemoglobin to 

 oxyhaemoglotrin, these being the characteristic blood pigments. 

 The easy change of carotin, C4oH56, to xanthophyll, C^HseC^, 

 and vice versa, and the reversible changes of the yellow anthoxan- 

 thins to the red anthocyanins, under the influence of the oxidizing 

 and reducing enzymes which are universally present in plants, 

 would indicate the possibility of the service of these pigments as 

 carriers of oxygen for respiratory activities in plants in a way 

 similar to that in which the blood pigments serve this purpose in 

 the animal body. The fact, which has been observed in con- 

 nection with the experimental studies of the development of the 

 lycopersicin, that tomatoes which normally would become red 

 remain yellow in the absence of oxygen, indicates that this pig- 

 mentation, at least, is definitely connected with oxygen supply; 

 and the further fact that the development of lycopersicin in red 

 tomatoes, red peppers, etc., is dependent upon the temperature 

 at which the fruit ripens, may indicate a definite connection of 

 this pigment with the need for more oxygen (or for more heat, as 

 suggested in the following paragraph) at these lower tempera- 

 tures. 



Again, many investigators have concluded that at least one 

 function of the anthocyanin pigments is to absorb heat rays and so 

 to increase transpiration and other chemical changes. In support 

 of this view,' there may be cited the general presence of such pig- 

 ments in arctic plants, their appearance in the leaves of many 

 deciduous trees after a frost in the fall, etc. Indeed, there is 

 much to support the view that the autumnal changes in foliage 

 pigments have the physiological function of absorbing heat in 

 order to hasten the metabolic processes of ripening and prepara- 

 tion for winter defoliation. The rapid and brilliant changes in 

 foliage coloring after a sharp frost which kills the tissues and makes 

 rapid translocation of the food material of the leaves to the 

 storage organs immediately necessary, have been explained as the 



