6o The Living Plant 



as will later appear, there is a probable adaptational advantage 

 in the compounding of leaves, since it aids them to resist the 

 tearing action of strong winds, and there is a possible adaptive 

 explanation of the deep lobing of leaves like Ivies and Maples 

 in the opportunity thus afforded for an interlocking of the leaves 

 and consequent utilization of every ray of the incident light. 

 But nobody, so far as I can find, has yet been able to give a reason- 

 able explanation of the significance of the emarginations of leaves, 

 for the suggestion that the points thus resulting serve to collect 

 atmospheric electricity for some use by the leaf can hardly be 

 seriously entertained. Emargination, lobing and compounding 

 are evidently three degrees of the same thing, but it is by no means 

 necessary to believe that because compounding is adaptively 

 useful, therefore emargination must be useful likewise. On the 

 contrary, it is not only possible that the emargination of leaves 

 originates non-adaptively in some manner purely incidental 

 or accidental, and is later intensified adaptively to lobing and 

 compounding, but the method embodied in this supposition affords 

 the most reasonable explanation we yet possess of the origin of 

 adaptations. 



While adaptation to the mode of exposure to light is the chief fac- 

 tor in determining the shape of the leaf, other adaptations and influ- 

 ences, very different in different cases, exert also their effects, 

 making the shape of any given leaf a resultant of the cooperation of 

 many influences. This fact the reader must remember when he 

 tries to apply the principles of the preceding pages to the ex- 

 planation of leaf shapes he may find in his walks abroad in the 

 country. At first he will find so many exceptions and contra- 

 dictions that he may incline to dismiss my explanations as ground- 

 less; but if he will continue his observations with patience, he 

 will gradually find the exceptions disappearing and the essentials 

 standing out in those composite conceptions of which I have 

 spoken in the first chapter; and then, I believe, he will agree 

 with the conclusions here expressed. 



