XI. FORMATION OF CARBOHYDRATES 



A . The Conditions Necessary for Carbohydrate Formation: 

 Experiment 25. To ascertain if light is necessary for 



carbohydrate formation. 



1. A green leaf, previously partly shaded by having a 

 strip of black cloth closely affixed to both sides, is 

 to be tested for starch as described under Experi- 

 ment 21, after having been in the sunlight for several 

 hours. Record as previously directed.* 



Experiment 26. Is chlorophyll necessary for carbo- 

 hydrate formation? 



2. As directed under Experiment 21, test a variegated 

 leaf, having white areas devoid of chlorophyll. 

 Make three drawings of the leaf, as follows: (a) 

 showing (by shading) the distribution of chloro- 

 phyll in the tissues; (b) showing the leaf decolorized; 

 (c) showing (by shading) the areas that gave the 

 starch reaction with iodine. 



B. E/ects of Light on Chlorophyll: 



Experiment 27. To show the need of sunlight for the 

 formation of chlorophyll by chloroplasts. 



1. Examine a seedling of any convenient plant that 

 has been allowed to develop in darkness. Compare 

 its color with that of another seedling of the same 

 species grown in daylight. 



2. Now place the seedling in diffuse sunlight for 

 twenty-four to forty-eight hours. Record the re- 

 sult, and state your inferences. 



*The "light screen," devised by Professor Ganong, for experiments in 

 starch formation by leaves, is specially recommended for this experiment. 



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