PRICKLES AND BRISTLES 



ID.-) 



W*i 



softer growth, so that the side buds do not have a chance 



to start. The thorns of osage orange and honey locust 



are also branches. Those of the honey locust usually 



arise from supernumerary buds which are 



borne somewhat above the axils. 



21G. Prickles, bristles, "ml weak spines, 



which havt a definite arrangement on the 



stmt, are usually >n<><lifi<<l leaves or parts 



of leaves. The spines of i56. Leaf-spine of' 

 thistles are hardened barberiy - 



points of leaf -lobes. The spines of the 

 barberry are reduced leaves; in their axils 

 are borne short branches or leaf -tufts 

 (Fig. 15G) ; in spring on young shoots 

 may be found almost complete gradations 

 from spiny leaves to spines. In the prickly 

 ash the prickles are stipules and stipels. 

 The reasons for interpreting them so are 

 apparent in Fig. 157. Stipular prickles 

 may also be seen in the common or aca- 

 cia locust ( robin ia I. 



217. Prickles, bristles, and hairs, which 

 art scatti red or 



i:,7. Stipular prickles h " r ' "" definite ">- 



of prickly ash. rangement, an usu- 

 ally men out-growths of the epi- 

 dermis. They usually are re- . 

 moved with the bark. Of such are ^C" 

 the prickles of squashes, briars 

 ( Fig. L58) . and roses. 



2is. Tim reason for the exis- 

 tence of spines Is difficult to de- 

 termine, in many or most cases 

 they seem to have qo distincl use or function. In some 

 way they are associated with the evolution of the plant. 



1 



L58, l'i ii ltl< 



