THE STRUGGLE FOR EXISTENCE. 



209 



on its midrib, as is the case "witli the nightshade shown in 

 rig. 87, and with so many roses. Prickles, which are merely 

 hard, shaxp-pointed projections from the epidermis, are of 

 too common occurrence to need illustration. 



Stipules are not infrequently found occurring as thorns, 

 and in our common locust, Fig. 188, the bud, or the very 

 young shoot, which proceeds from it, is ad- 

 mirably protected by the jutting thorn on 

 either side. 



251. Pointed, Barbed, and Stinging Hairs. 

 — Needle-pointed hairs are an efficient defen- 

 sive weapon of many plants. Sometimes 

 these hairs are roughened, like those of the 

 bugloss. Fig. 189, 6; sometimes they are 

 decidedly barbed. In the nettle. Fig. 189, 3, 

 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 considerable num- 

 bers in the skin of the hand or the face 

 after incautious contact with nettles, and 

 the intense itching which follows is only too 

 familiar to most people. 



252. Cutting Leaves. — Some grasses and 

 sedges are generally avoided by cattle because 

 of the sharp cutting edges of their leaves, which will readily 

 slit the skin of one's hand if they are drawn rapidly through 

 the fingers. Under the microscope the margins of such 

 leaves are seen to be regularly and thickly set with sharp 

 teeth like those of a saw. Fig. 189, 7, 8. 



253. Weapons of Desert Plants. — In temperate regions, 

 where vegetation is usually abundant, such moderate means 

 of protection as have just been described are generally suffi- 



FiG. 188. — Thorn 

 Stipules of Locust. 



