202 ■ SAGACITY AND MORALITY OF PLANTS. 



green bracts, so that petals are quite unnecessary. 

 The tropical Euphorbias are kept in our green- 

 houses for the sake of the striking colours which 

 their floral bracts develop. The BoiLgaimdlleay be- 

 longing to a widely separated order, has evolved a 

 similar method of floral attraction. This plant is 

 now very abundantly grown for the sake of its ex- 

 quisitely lovely pink flowers ; but each of the seeming 

 petals, on examination, prove to be altered bracts 

 or leaves, in which even the venation has not been 

 obscured. 



The purpose before me, however, is not to pro- 

 duce an inventory of all the botanical facts bearing 

 upon the political and social economy of plants, but 

 to draw attention to the operations of these prin- 

 ciples in the vegetable kingdom. 



Nowhere are they better exemplified than among 

 leaves. We have already seen that the latter are 

 vegetable units, and their plasticity is evidenced by 

 the readiness with which they can be metamorphosed 

 into carpels, stamens, petals, sepals, bracts, tendrils, 

 or thorns, as occasion may require. This, however, 

 does not interfere with the chief reason of their 

 existence, which is to assist in building up the tissues 

 of the parent -plant or common stock ; as well as 

 of preparing both for leaf-successors and plant- 

 continuance. 



When leaves are told off to do other work, the 

 plant must make some arrangements by which the 



