102 :©otani2 



Much as leaf-green has been studied, no one can 

 tell exactly of what it is made or how it performs its 

 work. We only know that the work is very well 

 done ; food and fresh air come freely to us from 

 these busy cells, the workshop of the leaf-green. 



A pale j'^llow pulp called etiolin is supposed to 

 precede the leaf-green. This sickly yellow is the 

 tint of most leaves in the bud, of the first unfolding 

 of cotyledons, and of plants grown in darkness. If 

 green j^lants are put into a dark, chilly place, their 

 leaf-green returns to the dull etiolin. 



The change made in such leaves by exposure to 

 light and warmth is very rapid. Take a potato 

 vine ; let it sprout in a cellar. It reaches out toward 

 the place where there is light, even if that comes but 

 from some little chink. Toward that light the pale 

 vine grows, no matter how it has to twist and turn 

 to do so. Let in stronger light somewhere, and very 

 soon it has changed its direction. 



A vine thus grown in darkness will be nearly 

 white, and also soft and watery. Place it in the sun- 

 shine ; in a few hours it will be green ; in a few days 

 dark green and firm of substance. A very few hours 

 will change the etiolin to full green, and the rapidity 

 of the change is in proportion to the sunlight given. 



From simple experiments we see that the pale 

 etiolin, which is formed chiefly from starch, is 



