Leaves. 8 1 



butter and wax, and expose the branch to the sunlight 

 until the uncoated leaves are found to contain starch. 

 Then test sections from the coated leaves, and if these are 

 found to be without starch, the inference is well founded 

 that this is due to the exclusion of carbon dioxide by the 

 closing of the stomata by the wax mixture. 



94. Strip the leaves from some thrifty plant, and pick 

 off new leaves as fast as formed. Note the result, and tell 

 how the final effect is produced. 



DISCUSSION. 



60. Prominence of Leaves. — We have seen that as soon 

 as the seedling appears above the ground its leaves unfold 

 and turn green, and that the subsequent development of 

 the shoot appears to consist mainly in the production of a 

 succession of green leaves arranged in a definite order around 

 the stem. When we look at a plant under normal condi- 

 tions, in the prime of its development, it is the wealth of 

 its foliage which impresses us most. In the whole family 

 of grass plants, with exceptions which do not need to be 

 considered here, the stem is very insignificant compared 

 with the leaves. When we contemplate the billows of leaves 

 in vast wheat and corn fields, and remember the rich har- 

 vests that are to follow, we must be impressed with the 

 supreme value of leaves in the life of the plant and in the 

 production of its seeds. Under normal conditions of mois- 

 ture, etc., we find many plants without stems above the 

 ground, but not without leaves. The superficial evidence 

 is therefore plain that leaves are of paramount value in 

 the economy of the plant. We shall see how true this is 

 when we consider the work done by them. 



61. Position of the Leaves. — We have observed that 

 the leaves are borne in a definite order on the stem. In 



