1 40 REASONS FOR THE DIFFERENCE. [CHAP. 



veins, had one central bundle. But I soon came 

 across numerous exceptions, and had to give up the 

 idea. I then considered whether the difference could 

 be accounted for by the mode of growth of the leaf, 

 and I am still disposed to think that it has some 

 bearing on the subject, though this requires further 

 study. 



The next suggestion which occurred to me was 

 that it might be connected with the " prefoliation " or 

 arrangement of the leaves in the bud. The first 

 palmate leaves which I examined were what is called 

 " plicate," or folded up more or less like a fan ; while 

 the leaves with pinnate veins were generally "con- 

 duplicate," or had the one half applied to the other. 

 But, though this was true in many cases, it was not a 

 general rule, and I was obliged to give up this idea 

 also. It then occurred to me to take climbing plants, 

 and see whether I could find any relation between 

 palmate and tongue-shaped leaves on the one hand, 

 and the mode of growth on the other whether, for 

 instance, the one turned generally up, the other down ; 

 whether the one were generally twining and the other 

 clasping, or vice versa. All these suggestions one by 

 one broke down. 



Among Monocotyledons, however, the tongue- 

 shaped preponderates greatly over the palmate form 

 of leaf. With very few exceptions, the form's of the 

 leaves of climbing Monocotyledons are in fact just 

 such as would be obtained by widening more or less 

 the linear, grass-like leaf which is so prevalent in 

 the class. 



This, then, raises the question whether the heart 



