THE STRUGGLE FOR EXISTENCE. 209 
on its midrib, as is the case with the nightshade shown in 
Fig. 87, and with so many roses. Prickles, which are merely 
hard, sharp-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 sufii- 
Fie. 188. — Thorn 
Stipules of Locust. 
