PROTEACEAE 145 



Leucadendron* argenteum (L.) R. Br. The Silver tree, 



Witteboom. 



(Plates 27, 28; Fig. 76.) 



The silver tree has a small area of distribution, 

 occurring naturally only on the Cape Peninsula, while the 

 patches on various hills of the Paarl and Stellenbosch districts 

 are, in our opinion, due to dissemination by the hand of 

 man. On the slopes of Table Mountain, the Lion's Head 

 and the Devil's Peak, or the mountains further south, it 

 always occupies very windy and comparatively dry 

 situations, where soft-leaved trees or shrubs cannot persist 

 in summer, especially not during a prolonged period of 

 South East wind. It is, however, just at such times that 

 the silver tree shines more brilliantly than usual. 



This beautiful gloss the leaves owe to their coat of 

 fine silky hairs, with which nature has provided them on 

 both sides as a protection against excessive transpiration 

 during dry weather, and it is remarkably well adapted to 

 this function. 



In winter or during other rainy weather the hairs on 

 the surface of the leaf (Fig. 76, A, 2) are half raised, forming 

 an angle of about 30 degrees with it and consequently 

 allowing the air to circulate freely between them and to 

 diffuse in and out through the stomata. In dry weather, 

 however, and especially when strong winds exert their 

 exhausting influence on the vegetation, the hairs move 

 downwards by means of the basal cell which collapses on 

 one side, acting like a hinge (Fig. 76, A, 2). The hairs are 

 thus tightly pressed against the leaf, forming a continuous 

 layer and shutting off completely communication between 

 the tissue of the leaf and the atmosphere. To this 

 movement the brilliant optical effect is due. The smooth 

 layer of glossy hairs naturally reflects the light more 

 strongly than the rough surface formed by their projecting 



* Although grammatically incorrect the spelling as originally published must be 

 adhered to. Linnaeus, Bergius, Robert Brown and others write it as above. 



m. 19 



