168 LEAVES 



Also test monocotyl plants like ribbon grass, tradescan- 

 tia, etc., which have their leaves streaked with white. Do 

 the monocotyls give equally good tests for starch? How 

 do you account for the difference? Test the same plants for 

 sugar. Result ? 



Query. What has 'been shown in previous exercises as 

 to the necessity of light for growth of plants ? How does 

 light affect the direction of growth of stems ? The position 

 and arrangement of leaves? The vigor of plants? The 

 color and size of leaves? What substance do leaves absorb 

 from the air? Does this take place equally in the light 

 and darkness f What substances are given off by leaves ? 

 Give proofs for each substance mentioned. What sub- 

 stances are manufactured by leaves? Can these substances 

 be made in darkness? What part of the leaf makes the 

 starch? By what energy? Out of what substances? 

 What waste product is set free at the same time? 



151. LEAVES 



Object. To observe the effect of closing up the sto- 

 m>ata of a leaf- 



Apparatus. Any healthy plant, preferably one of the common 

 deciduous plants, and vaseline. 



Method. Without removal from the stem coat both sur- 

 faces of a leaf with vaseline, being sure to cover all stomata. 

 After three or four days apply tests for starch and sugar. 

 What result? 



Conclusion. State whether air is needed by a leaf to 

 make starch. 



Query. How may this be explained ? What happens to 

 a leaf which has been coated with vaseline if allowed to re- 

 main attached to the stem ? 



