XVl] PRICKLES, THORNS, ETC. 127 



of the Wayfaring Tree, looking as if sprinkled with ashes 

 or flour, is due to branched hairs, and somewhat similar 

 stellate hairs occur on the Plane. 



When hairs are quite absent, the surface is said to be 

 glabrous, a term which does not necessarily mean smooth, 

 however, since the hairless surface may be thrown into 

 folds (rugose or wrinkled), or fissured, striate, &c., in various 

 degrees. In many cases the smooth surface is also shining, 

 glistening or polished. 



More prominent outgrowths of the epidermis are the 

 bristles and prickles of the Roses, Blackberries and those 

 occasionally found on the internodes of the Gooseberry. 

 These are essentially of the same nature as hairs, but they 

 are much larger and obvious structures. The best simple 

 sign of their superficial character is afforded by the ease 

 with which they can be pushed off the surface by a 

 lateral pressure, when it is seen that they usually come 

 away leaving a scar, and without bringing off any of the 

 underlying tissues. 



Other kinds of spinose organs are the pointed out- 

 growths of the leaves of the Holly, and of Berberis, &c., 

 where all the tissues are concerned in their formation, 

 and which cannot be removed without doing injury to the 

 internal structure of the leaf. 



Totally different from the above, in origin and in details 

 of structure, are various kinds of spines and thorns, the 

 nature of which is best discovered by the relations of 

 position which they show as regards the buds and leaves, 

 or leaf-scars, on the branches. A true thorn is a sharp- 

 pointed woody structure which either terminates the twig, 

 or is itself a short twig or dwarf-shoot. In the first case 

 its proper character comes out from the fact that it bears 

 buds and leaf-scars lower down on the same axis ; in the 

 second case we have the additional evidence that it arises 



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