PRICKLES, THORNS, AND STINGING HAIRS 417 



Prickles, which are merely hard, sharp-pointed projections 

 from the epidermis, are of too common occurrence to need 

 illustration. 



Thorns are often found to be modified stipules, and in our 

 common locust (Fig. 319) the bud, or the very young shoot 



FIG. 319. Thorn 



stipules of 



locust 



FIG. 318. Euphorbia splendens 



The spines are dead and 

 dry stipules 



which proceeds from it, is admi- 

 rably protected by the jutting thorn 

 of the previous year on either side. 



389. Pointed, barbed, and sting- 

 ing hairs. On many plants needle- 

 pointed hairs form efficient defensive weapons. 

 Sometimes these hairs are roughened, like those of the bugloss 

 (Fig. 320, &); sometimes they are decidedly barbed. If the barbs 

 are well developed, as they are in the small but formidable 

 bristles of prickly pear cactuses, they may cause the hairs to 

 travel far into the flesh of animals and cause intense pain. In 

 the nettle (Fig. 320, a) the hairs are efficient stings, with a 

 brittle tip, which on breaking off exposes a sharp, jagged tube 

 full of irritating fluid. These tubular hairs, with their poisonous 

 contents, will be found sticking in the skin of the hand or the 

 face after incautious contact with nettles, and the violent itch- 

 ing which follows is only too familiar to most people. 



