i8 The Living Plant 



habit, as the list above given will testify, contenting themselves 

 with the odd and obscure places of nature, while the green plants 

 grow grandly in stature and number, possessing the earth. And 

 still a third difference exists, less likely to be thought of but no 

 less important for our present inquiry, namely, the study of 

 classification has shown that the non-green plants, for the most 

 part at least, are descended in the course of a long evolution 

 from green ancestors, and therefore have been green in the past. 

 Hence we are brought to a generalization of the greatest impor- 

 tance, the first indeed of the great botanical verities, the pos- 

 session of chlorophyll is a well-nigh universal characteristic of 

 plants, and their most distinctive feature. 



Such is the notable fact concerning the occurrence of chloro- 

 phyll in nature. Obviously so wide-spread a substance must 

 play some very great part in the life processes of plants, and it is 

 our manifest duty to determine what it is. In any such study 

 the first resort of the biologist, his first aid, as it were, to his 

 ignorance, is observation, exact and interrogative observation, 

 of so much as the eye can discover. If, now, the reader will look 

 over, from this point of view, any collection of plants in garden or 

 greenhouse, drawing meanwhile on his memory for additional 

 facts from his own experience, he will find these things to be true; 

 that chlorophyll is not omnipresent in those plants which pos- 

 sess it, being absent from their roots and interior parts not reached 

 by the light: that even in lighted parts it is not uniformly dis- 

 tributed, being denser in the better-lighted places, as well ex- 

 emplified in the deeper green of the upper as contrasted with the 

 lower faces of leaves: that it does not develop at all in leaves 

 which are grown out of the light, as witness the colorless sprouts 

 of potatoes started in the darkness of cellars, or the grass of lawns 

 accidentally left covered in spring: that it vanishes from green 

 parts kept away some time from the light, as shown in the blanch- 

 ing of celery when banked up with earth: and that most green 

 parts turn over towards light when this comes rather strongly 



