650 CONSERVATIVE ORGANS. [LECT. XI. 



(rectij, that is, free from any curvature, and di- 

 minishing gradually from the base to the apex, as 

 on the Scotch Rose, Rosa spinosissima ; or curved 

 (curvi), as on the Bramble, Rubusfruticosus. If 

 the curved prickle have its point directed up- 

 wards, it is said to be incurved (incurvus vel in- 

 Jlexus), and if in the opposite direction, recurved 

 (recurvus vel reflexus). It is, also, in some 

 instances spiral (circinnatus) , with the apex 

 turned inwards, as in the genus Hugonia. Like 

 the thorn, the prickle is simple or compound, ac- 

 cording as it has one or more points ; and it is 

 termed caulinar, petiolar, or foliar, from its si- 

 tuation being on the stem, or on the branch, the 

 petiole or the leaf. It is in general solitary ; but 

 in some plants prickles are always found in pairs 

 (geminati) ; and on others, as for example the 

 Barberry, Berberis vulgaris, several stand together 

 on the same plane, and are said to be palmated 

 (palmati). Prickles consist of condensed cellular 

 matter covered with an epidermis, which becomes 

 dry, hardj, and coloured with age. They originate 

 immediately under the cuticle; and when picked 

 off leave no impression deeper than the exterior 

 layer of the bark. Indeed in the majority of in- 

 stances they appear to be productions of that layer, 

 and consist altogether of a mass of oblong cells, 

 which become more condensed and tubular as 

 they approach the point, and over which the 



