vi.J LOBSD AND HEART-SHAPED LEAVES. 139 



flower. For a weak plant growing among close grass, 

 a long linear leaf is, perhaps, physically an advantage ; 

 but one may venture to suggest that the leaves would 

 be more likely to be picked out and eaten if they 

 were more easily distinguishable, and that from this 

 point of view also the similarity of the plant to the 

 grass among which it grows may also be an advantage. 



In looking at foliage I have often been much 

 puzzled as to why the leaves of some species are 

 tongue-shaped, while others are lobed. Take, for 

 instance, the black Bryony (Tamus communis) and 

 the common Bryony (Bryonia dioicd}. Again, why 

 are the veins in some leaves pinnate, like those of the 

 Beech and Elm, and others palmate, as in the Maple 

 and Sycamore ? 



My first idea was that this might have reference to 

 the arrangement of the woody fibres in the leaf-stalk. 

 If we make a section of the stalk of a leaf, we shall 

 find that in some cases the woody fibres are collected 

 in the middle, while in others there are several distinct 

 bundles, separated by cellular parenchyma. My first 

 idea was that each of the primary ribs of a leaf might 

 represent a separate woody fibre in the leaf-stalk, so 

 that leaves with a single bundle of woody fibres 

 would be pinnate ; those with several distinct bundles 

 palmate. 



The first species which I examined favoured this 

 view. The Melon, Geranium, Mallow, Cyclamen, and 

 other species with palmate leaves had, sure enough, 

 several woody fibres; while, on the contrary, the 

 Laurel, Rhododendron, Privet, Beech, Box, Castanea, 

 Arbutus, Phillyrea, and other leaves with pinnate 



