THE PROBABLE ORIGIN OF KEY-FRUITS. 233 



THE PROBABLE ORIGIN OE KEY-FRUITS. 



By H. Tullsen. 



In late autumn and in winter, long; after the leaves have 

 fallen, we are apt to see still clinging to the trees some of the 

 foliaceous seed-vessels— called samaras, or key-fruits — of certain 

 maples and ash-trees. These trees are not closely allied, but the 

 external structure of the fruit, /. e., the wing, is much the same in 

 the one case as in the other, indicating that the function thereof is 

 identical in both. The wing is present for the purpose of serving 

 as a sail against which the wind shall act and blow the seed far 

 away to be planted in new soil. The fruit of the ash consists of 

 one samara, while that of the maple consists of two, and these are 

 ultimately separable. 



There are about one hundred species of maples {Acer) and 

 forty species of ash {Fra.nnus). All have winged fruits. We 

 may be certain that this peculiar form of fruit was not developed 

 independently in each of these numerous species. In order so to 

 believe we should have to expect too much of chance. In the case 

 of the maples it was inherited from some ancient aceriform pro- 

 genitor, which, through natural selection, had taken to the pro- 

 duction of winged fruits; and an old-time fraxinoid tree, also 

 bearing this sort of fruit, was the ancestor of our present-day 

 ash-trees. 



The direct action of the environment can have done nothing 

 towards the development of the foliaceous fruits of the trees under 

 consideration. It would be hard to conceive of any other factor 

 than natural selection as having wrought to produce them. Nat- 

 ural selection, we know, can operate only where there prevails a 

 fierce and keen struggle for existence. So, in some great struggle 

 of the past, we may conclude that the production of winged seed- 

 vessels, by insuring the wider territorial distribution of the trees 

 that bore them, saved the ancestors of the maples, and those of 

 the ash, from extinction. 



