THE WORK OF LEAVES 183 



The cork or tin -foil must not be applied so closely as 

 to prevent the free circulation of air between it and 

 the leaf. The leaves must not be removed from the 

 plant and should be placed where they may obtain 

 abundant sunlight; Nasturtium leaves may be recom- 

 mended for this experiment. In two or three days test 

 for starch. 



Now of what use is the starch in the foliage- 

 leaves ? Is it absorbed by the plant, like the starch in 

 the seed-leaves ? If so, ought we not to find less starch 

 in the leaves in the morning than at sundown (since 

 the starch which is taken away from the leaf during 

 the night cannot be replaced until it is again exposed 

 to light)? Remove some leaves from a plant near sun- 

 down and place them in alcohol; early the next morn- 

 ing remove some more leaves from the same plant and 

 test both sets of leaves for starch. We may also make 

 the experiment by cutting out a sample from a leaf at 

 sundown, to be compared with a sample taken from 

 the same leaf the next morning. Has the starch disap- 

 peared ? Would it have done so had the leaves not 

 been left on the plant? Repeat the experiment, but cut 

 the leaves off and leave them over night in a tumbler 

 of water (the stalks must dip well under the water) . 



It is now time to see whether we can answer the 

 question, Why are the foliage-leaves and seed-leaves (of 

 the Horse-bean) so different? You can see that it is of 

 advantage to the plant to have the foliage -leaves re- 



