THJ£ LEAF 



81 



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

 formed; and that floating leaves are free tij acquire this 

 shape because tliey do not oversliade 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 whicli 



1 ■, 1 • -1 (l(j. Leaf of llie Talii") Tree (Liriodendron) . 



admit carbonic acid gas ' 



and oxj'gen are in this upper surface. Th(; circular Ijliide 

 with the petiole attached near the center is well adapted 

 to Iceeping every part afl<.iat. 



137. The influence of the mode of fold- 

 ing of the blade in the bud on its final 

 sliape is well illustrated by the leaf of the 

 Tulip tree (^Liriodendron, Fig- 60). The 

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

 it were, or truncate. There are also pro- 

 jections, or loheis, on either side. Figure 

 68 shows liow the lobes, and recesses, and 

 the truncation lit tlie space which the very 

 young blade occupies between and around 

 other parts of the dc\eloping bud. Fig- 

 ure 67 shows the blade, witli its two 



nr. Winter bud o£ lialvcs flatly folded together, in the win- 

 ter bud. 



138. The benefit of equal illumination 

 fur all the leaves may well be the causi' 



Winter bud of 

 Liriodendron, 

 with some 

 of the outer 

 scales turned 

 back. 



OUT. OF EOT. 6 



