THE AXGIOSPERMAE : LEAVES 1035 



the margins of the lamina, to completely reduced, non-chlorophyllous spines, 

 such as the larger spines of Opuntia and other Cacti, which are considered 

 to be extremely modified leaves. 



Intermediate conditions are conunon. Small leaves or phyllodes ending 

 in a sharp point are scarcely to be distinguished from spines (Fig. 1027). 

 The same plant may produce both typical flattened leaves and cylindrical 

 spinose ones, as in many species of Hakea, or individual leaves may change 

 from an assimilator\' function to spines as they grow older. I'his happens 



Fig. 1026. — Acer pseudoplatanus. Portion 

 of a stem showing V-shaped leaf scar 

 and axillary bud transformed into a 

 winter bud. 



in some Leguminosae, notably species of Astragalus, where the leaflets of 

 the compound pinnate leaf drop off, while the rachis persists and becomes 

 a long spine. The pinnately divided leaves of the climbing Palm, Calamus, 

 show a gradual transition from the foliar to the spiny condition as the tip 

 of the verv long rachis is approached (Fig. 1028). I'he spiny segments are 

 directed obliquely backwards and are, in this case, the plant's chief means 

 of attaching itself to its supports in climbing. 



The genus Berheris shows a curious relationship of leaves and spines. 

 At the base of young shoots each node bears a single leaf, usually with a 

 spiny margin, and two small stipules. Higher up the shoot the leaves diminish 

 in size, the marginal spines becoming more prominent, until they are reduced 

 to one or sometimes three spines. The stipules elongate and likewise become 



