CHAPTER XL 



CHLOROPHYLL AND THE FORMATION OF STARCH. 



154. In our experiments thus far in treating of the absorption 

 of carbon dioxide and the evolution of oxygen, with the accom- 

 panying formation of starch, we have used green plants. 



155. Fungi cannot form starch. — If we should extend our 

 experiments to the fungi, which lack the green color so charac- 

 teristic of the majority of plants, we should find that carbon con- 

 version does not take place even though the plants are exposed 

 to direct sunlight. These plants cannot then form starch, but 

 obtain carbohydrates for food from other sources. 



156. Etiolated plants cannot convert carbon. — Moreover 

 carbon assimilation is usually confined to the green plants, and 

 if by any means one of the ordinary green plants loses its green 

 color carbon conversion cannot take place in that plant, even 

 when brought into the sunlight, until the green color has 

 appeared under the influence of light. 



This may be very easily demonstrated by growing seedlings 

 of the bean, squash, corn, pea, etc. (pine seedlings are green even 

 when grown in the dark), in a dark room, or in a dark receiver 

 of some kind which will shut out the rays of light. The room 

 or receiver must be quite dark. As the seedlings are "coming 

 up," and as long as they remain in the dark chamber, they will 

 present some other color than green; usually they are somewhat 

 yellowed. Such plants are said to be etiolated. If they are 

 brought into the sunlight now for a few hours and then tested 

 for the presence of starch the result will be negative. But if the 

 plant is left in the light, in a few days the leaves begin to take 



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