i62 VIGNETTES FROM NATURE. 



roads in the plains, and rise in a solid wall to 

 a height of fifteen or twenty feet. No animal 

 on earth dare attempt to pass through such a 

 hedge; and the task of cutting one down, 

 when necessary, is extremely difficult. On 

 bare dry expanses, like the Mexican plain, 

 cactuses and agaves run wild in every direc- 

 tion, collecting what little moisture they can 

 in their thick stems or big succulent leaves, 

 and defending it against herbivorous enemies 

 by their formidable spines. To prevent eva- 

 poration, they are covered by a thick and 

 very firm epidermis, so that they lose very 

 little of their moisture even during months of 

 drought. . 



What these great desert plants do on a 

 large scale, our little English saltv/ort does 

 on a much smaller scale. It has the same 

 strong prickles, the same thick, juicy leaves, 

 the same protective epidermis, and the same 

 general aspect or habit of growth as the 

 cactuses themselves. If one were to enlarge 

 it tvventyfold, every casual observer would 



