THE LEAF 



81 



matters to and from the leaf stalk is most easily per- 

 formed; and that floating leaves are free to acquire this 

 shape because they do not overshade one another. 



136. Again, the rounded forms are plainly better bal- 

 anced, ride the waves better, and are less likely to be 

 tipped and partially 

 submerged. It is im- 

 portant that the upper 

 surface of floating leaves 

 should be kept free, as 

 is shown by the fact 

 that they are coated 

 with a waxy substance 

 which prevents wetting, 

 and which causes water 

 thrown upon the leaves 

 to roll away in all direc- 

 tions. The pores which 

 admit carbonic acid gas Leaf ' *e Tulip Tree (Uriodendron). 

 and oxygen are in this upper surface. The circular blade 

 with the petiole attached near the center is well adapted 

 to keeping every part afloat. 



137. The influence of the mode of .fold- 

 ing of the blade in the bud on its final 

 shape is well illustrated by the leaf of the 

 Tulip tree (Liriodendron, Fig. 66). The 

 end of the lamina is seen to be cut off, as 

 it were, or truncate. There are also pro- 

 jections, or lobes, on either side. Figure 

 68 shows how the lobes, and recesses, and 

 the truncation fit the space which the very 

 young blade occupies between and around 

 other parts of the developing bud. Fig- 

 ure 67 shows the blade, with its two 



67. winter bud of halves flatly folded together, in the win- 



Liriodendron, , , 



ter bud. 



138. The benefit of equal illumination 



for all the leaves may well be the cause 



with some 

 of the outer 

 scales turned 

 back. 



OUT. OF HOT. 6 



