152 LIVING PLANTS 



plant is greatest in an atmosphere containing 

 two hundred times as much, seven to ten per 

 cent by volume. The power of using larger 

 proportions of carbon dioxide was doubtless 

 acquired in an earlier geologic period, and was 

 adapted to the conditions then prevalent. 



The botanist finds himself lost in a maze of 

 conjecture if he endeavors to trace backward 

 the development of plants and determine the 

 Acquisition of point at which they gained the power to form 

 chlorophyU chlorophyll. It is quite certain that the simpler 



ancestral forms, which consisted of simple 

 masses of protoplasm, were not able to con- 

 struct and maintain a substance so complex 

 and unstable as chlorophyll. The advent of 

 this substance into the living world marked 

 the attainment of a comparatively advanced 

 stage of development. A tinge of probability 

 lends itself to thetheor3^ that the protoplasm 

 of all simple organisms which existed in a far 

 distant age of the world's history were able 

 to accomplish the synthesis of complex from 

 simple compounds, and that the "sulphur" 

 and "iron" bacteria are but remnants of this 

 primitive physiological type. 



Still another problem is to be found in the 

 presence of chlorophyll in a number of the 

 lower forms of animals. A fact which renders 

 the task of making categorical distinction be- 

 tween plants and animals still more difficult. 



