FROM THE ATTACKS OF ANIMALS. 13? 



But the most important means of defence to the 

 plant against hungry animals are organs which run 

 out into sharp, protruding points, ready to wound 

 an aggressor. We may call these the weapons of 

 the plant. They may be divided botanically into 

 thorns and prickles. A thorn is an organ which 

 runs out into a sharp spine, composed principally 

 of woody tissue, or traversed by fibrovascular bun- 

 dles. A prickle is an outgrowth from the skin of 

 a plant, without woody bundles, one-celled or many- 

 celled, always ending in a sharp point, capable of 

 wounding an assailant. This distinction is not an 

 important one and cannot always be maintained. 



Spines and prickles appear on every possible 

 portion of a plant. They are generally above or 

 near the green tissue which they protect, but often 

 the path leading to the green parts over leaf- 

 stalks, stem, and sometimes aerial roots, is pro- 

 vided with prickles and thorns, in order to keep 

 off the crawling creatures that eat the leaves, 

 especially the snails. The lower parts of the stem 

 up which they must climb to reach the green tissue 

 are armed with thorns and prickles in many plants, 

 as in Locusts and Roses. 



It is a very interesting fact that many woody 

 plants are armed only while they are low, and 



