HOW PLANTS PROTECT THEMSELVES 



349 



417. Plants with Weapons for Defense. 1 Multitudes 

 of plants, which might otherwise have been subject to the 

 attacks of grazing or browsing animals, have acquired 

 what have with reason been called weapons. Shrubs and 

 trees not infrequently produce sharp-pointed branches, 

 familiar in our own crab-apple, wild plum, thorn trees, 

 and above all in the honey locust (Fig. 34), whose formida- 

 ble thorns often branch in 



a very complicated man- 

 ner. 



Thorns, which are 

 really modified leaves, are 

 very perfectly exempli- 

 fied in the barberry (Fig. 

 243). It is much com- 

 moner to find the leaf 

 extending its midrib or 

 its veins out into spiny 

 points, as the thistle does, or bearing spines or prickles on 

 its midrib, as is the case with the nightshade shown in Fig. 

 244, 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. 246) the bud, or the very 

 young shoot which proceeds from it, is admirably pro- 

 tected by the jutting thorn on either side. 



418. Pointed, Barbed, and Stinging Hairs. Needle- 

 pointed hairs are an efficient defensive weapon of many 

 plants. Sometimes these hairs are roughened, like those 



1 See Kerner and Oliver's Natural History of Plants, Vol. I, p. 430. 



FIG. 244. Leaf of a Night- 

 shade (Solatium atropur- 

 pureurri). 



