I30 SAGACITY AND MORALITY OF PLANTS. 



that very protection which so effectually screens them 

 now from animal foes. 



The secretion of silica, which we sometimes find 

 in inordinate quantities in the leaves and stems 

 of plants widely separated by natural affinities, is 

 only understood when we know what an effectual 

 protection it is from caterpillars and other depre- 

 dators. Among familiar plants it is perhaps most 

 abundant in the cuticles of the Horsetails {Eqidseta- 

 cece), and various species of grasses, sedges, etc. The 

 "Dutch -Rush" {Eqidsetttm hyernale) was formerly 

 imported into this country for the purpose of polish- 

 ing metals, which quality it owed entirely to the 

 silica in its composition. The Equisetums are doubt- 

 less allied to the ancient Carboniferous Catamites, 

 and the genus Equisetum itself has probably been 

 in existence since the Oolitic Period. Possibly the 

 species owe their preservation because they have 

 learned to secrete silica ; just as we have surmised 

 ancient types of Ferns have been perpetuated through 

 their possessing tannin. 



Many species, including the Bamboo and other 

 Grasses, Canes, Palms, etc., must be favourably ad- 

 vantaged by their ability to secrete a mineral sub- 

 stance so disliked by animals as silica is. Many 

 of the leaves of our common British Grasses, such 

 as the Tufty -hair Grass (Aira coespitosd), abounding 

 usually in damp meadows and shady woods, contain 

 it so largely that no cattle eat it from choice. A 



