142 OUTLINES OF PLANT LIFE. 



Darken portions of some leaves of a plant previously found to show 

 starch in its leaves * (sunflov^er, bean, tomato, or nasturtium) by attach- 

 ing two plates of cork on opposite sides by means of two pins driven 

 through both and the leaf. On the afternoon of the following day, ii 

 sunny, cut ofi the leaves and test for starch as before. What has become 

 of starch in cells under the cork ? 



193. (c) Potassium salts. — These take no part in the 

 composition of the food produced, and their exact role is not 

 understood. It is well established, however, that their pres- 

 ence is essential to the formation of the carbohydrate food. 



194. Proteids. — The foods thus formed are sooner or later 

 built up into still more complex foods, the proteids. The 

 process by which this is accomplished is even more obscure 

 than the preceding, neither the steps in the process nor its 

 conditions being known. The formation of proteids occurs 

 abundantly in green leaves while they are illuminated, and 

 therefore making sugar, etc. But even in green plants pro- 

 teids are made in other parts than leaves, and in darkness. 

 They are also formed by colorless plants. Proteids are used 

 directly in the repair of the protoplasm, and for making new 

 protoplasm. 



E. Storage and transfer of food. 



195. Storage and transfer. — Both in the colorless and 

 green plants it is necessary that the foods should be trans- 

 ferred from the point where they are made or absorbed to the 

 place where they are to be used. The larger the plant, the 



* To ascertain this, test as follows : Boil a few leaves of various plants 

 for a few minutes. Place in alcohol at about 6o° C. until all chlorophyll 

 is dissolved. (Do not heat over open flame, but set tmttle, loosely corked, 

 in a vessel of hot water. ) Bring the leaves into a tincture of iodine, 

 diluted to a bright brown, for half an hour. The leaves or parts con- 

 taining starch will become bluish, dark blue, or black, according to 

 amount of starch present. 



