124 



ESSENTIALS OF BOTANY 



attacks of grazing or browsing animals, have acquired what 

 have with reason been called weapons. Among the most 

 conspicuous of these are thorns, which are often modified 

 branches. Thorns, which are really modified leaves, are 

 very perfectly exemplified in the barberry (Fig. 88). It 

 is much commoner to find the leaf extending its midrib or 

 its veins out into spiny points, as the thistle does, or bear- 

 ing spines or prickles on 

 its midrib, as is the case 

 with the nightshade 

 shown in Fig. 89, and 

 with so many roses. 



Stipules are not infre- 

 quently found occurring 

 as thorns, and in our com- 

 mon locust (Fig. 91) the 

 bud, or the very young 

 shoot which proceeds from 

 it, is admirably protected by the jutting thorn on either side. 

 145. Pointed, Barbed, and Stinging Hairs Needle- 

 pointed hairs are an efficient defensive weapon of many 

 plants. Sometimes these hairs are roughened, like those 

 of the bugloss (Fig. 92, 5); sometimes they are decidedly 

 barbed. If the barbs are well developed, they may cause 

 the hairs to travel far into the flesh of animals and cause 

 intense pain. In the nettle (Fig. 92, 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 incau- 

 tious contact with nettles, and the violent itching which 

 follows is only too familiar to most people. 



Fig. 89. Leaf of a, 

 Nightshade {Solanum 

 atropurpureum) . 



