416 



HOW PLANTS PROTECT THEMSELVES 



388. Plants with weapons for defense. 1 Multitudes of plants, 

 which might otherwise have been subject to the attacks of graz- 

 ing 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. 35), 



FIG. 316. Spiny leaves of barberry 



whose formidable thorns often branch in a very complicated 

 manner. It is noteworthy that the protection given by thorns 



is not from those of the 



season, but from the dry 



i/ 



and hard ones of preceding 

 years. 



u 



Leaves modified into 

 thorns are very perfectly 

 exemplified in the barberry 

 (Fig. 316). It is much com- 

 moner, however, 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 some night- 

 shades (Fig. 317) and with so many roses. 



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



FIG. 317. Spiny leaf of a 

 nightshade (S ilanum 

 atropurpureum) 



