76 FAMILIAR TREES 



a narrow green adherent stipule and a stalked gland. 

 In the presence of bud-scales, of honey-glands, and of 

 stipules to all the leaves, in texture, surface, colour, 

 and lobing, this species presents a marked contrast to 

 the Wayfaring-tree. Lord Avebury points out that 

 stipules are the exception in the Order Gaprifoliacece, 

 the Elder, and a few species of Viburnum, being 

 almost the only cases in which they are found. In 

 the majority of species of Viburnum the leaves are 

 unlobed and have no stipules: in the few that are 

 lobed, like the Guelder-rose, stipules are always 

 present, which obviously suggests a causal relationship 

 between lobes and stipules. When leaves are enclosed 

 in leathery bud-scales it is, Lord Avebury points out, 

 advantageous that the true leaves should be so folded 

 as to occupy less space, whilst he suggests that the 

 lobing of the leaf is a direct mechanical result of this 

 folding, and that the stipules are themselves a further 

 result of similar causes. " A leaf folded up as are 

 those of V. Opulus, requires," he says, " only two or 

 three lateral veins. The remaining veins, then, and 

 the membrane connecting them, will gradually be 

 reduced, and ultimately disappear." 



This is merely an application of a principle known 

 as the law of economy of nutrition, which has 

 been recognised from the time of Aristotle, and of 

 which we shall have something more to say presently 

 in another connection. The bases of the leaf-stalks in 

 the bud of the Guelder-rose are not dilated as are 

 those of the Wayfaring-tree, and there is accordingly 

 a space between them. This is usefully occupied by 

 the stipules. Thus scales and folding more than 



