20O SAGACITY AND MORALITY OF PLANTS. 



submerged leaves of water-plants belonging to the 

 most widely separated of orders can be explained by 

 the fact that all are alike subjected to the same 

 physical conditions of poverty, as regards carbonic 

 acid food -supplies. All such submerged leaves are 

 accordingly reduced to a minimum of size, to save 

 vegetal energy on the part of the parent-plants. 

 But several so-called species of more or less aquatic 

 Water -Crowfoots have two or even more sets of 

 leaves, according to physical circumstances. Ordi- 

 narily, those of their leaves exposed to the air are 

 expanded in the usual fashion, whilst those sub- 

 merged are restricted in their development to mere 

 mid-ribs and veins, resembling a cluster of green 

 threads. Our British species of Ranunculuses shows 

 every stage of transition, from the water-feeding to 

 the air-feeding leaves ; so that no more interesting 

 genus of plants for evolutionistic purposes occurs in 

 the British flora. (See Figs, 'j^, 77, 78.) 



In one order of plants, the Etiphorbiacece, the 

 usual accessories of a true flower are absent alto- 

 gether, and mere bracts, or altered leaves, have been 

 pressed into the new service to do the ordinary duty 

 of petals. How well they effect it is seen best of 

 all in the scarlet Poinsettia. No Poppy, with the 

 most orthodox of petals, is more colourably promin- 

 ent. Even our British Spurges, such as Euphorbia 

 helioscopica, E. portlandica, E. amygdaloides, and 

 others, have their flowers resplendent with golden- 



