STUDIES OF SEED-PLANTS 195 



the leaf-stalk, similar to the attachment of fingers to the 

 palm of the hand. 



Either type of compound leaves may have the leaflets 

 again divided one or more times, as on young shoots of honey- 

 locust, in meadow-rue, carrot, and parsnip. Compare carrot 

 and parsnip leaflets. 



Compare pinnately compound leaves with the pinnate 

 veining in simple leaves, such as elm. Compare a palmately- 

 veined simple leaf, as that of maple, with a palmately com- 

 pound leaf with five leaflets. Such comparisons suggest 

 that the leaflets of compound leaves correspond to the lobes 

 or divisions of simple leaves, of which there are all gradations 

 from small notches as in elm leaf and lobes as in oak leaves 

 to such extreme division as in the celandine, French mari- 

 gold, and ragweed. These latter are almost compound, but 

 show narrow strips of the blade connecting the divisions. 



Obviously, it is often difficult to distinguish between simple 

 and compound leaves, for there are many simple leaves so 

 deeply divided as to resemble closely compound leaves. 

 The only reason for attempting to distinguish in such cases 

 is for convenience in describing and identifying plants. So 

 far as functions are concerned, the compound leaves and 

 the deeply divided simple leaves are apparently equally 

 efficient in permitting light to reach lower leaves. Observe 

 such plants as carrots and ragweed in bright sunshine, and 

 note how the light filters through the clefts and reaches 

 lower leaves. Moreover, since breezes frequently sway the 

 leaves, and the position with reference to light constantly 

 changes with that of the sun, the result is that lower leaves 

 are quite sure to get more or less direct illumination each 

 day. Undivided leaves which exposed the same surface 

 on the same branch arrangement would certainly keep many 

 of the lower leaves in shade most of the time. 



