2 INTRODUCTION. 



The same may be said of plants ; for we can hardly point 

 to a single portion of the earth's surface which is not 

 tenanted by some vegetable form whose structure is 

 wonderfully adapted to its situation and requirements. 

 Even in the hottest thermal springs, and on the eternal 

 snows of the arctic regions, peculiar forms of vegetation 

 have been found. From the deepest recesses of the 

 earth to which the air can penetrate, to the summits of 

 the loftiest mountains ; from the almost unfathomable 

 depths of the ocean to the highest clouds; from pole to 

 pole, the vast stratum of vegetable life extends ; while 

 it ranges from a temperature of 35 to 135 Fah., a 

 range embracing almost every variety of conditions and 

 circumstances. 



The most cursory and superficial glance will recognise 

 in every scene a class of plants whose singular appear- 

 ances, habits, and modes of growth so prominently dis- 

 tinguish them from the trees and flowers around, that 

 they might seem hardly entitled to a place in the vege- 

 table kingdom at all. On walls by the wayside, on 

 rocks on the hills, and on trees in the woods, we see 

 tiny green tufts and grey stains, or parti-coloured rosettes 

 spreading themselves, easily dried by the heat of the sun, 

 and easily revived by the rain. In almost every stream, 

 lake, ditch, or any collection of standing or moving 

 water, we observe a green slimy matter forming a scum 

 on the surface, or floating in long filaments in the depths. 

 On almost every fallen leaf and decayed branch, fleshy 

 gelatinous bodies of different forms and sizes meet our 

 eye. Sometimes all these different objects appear grow- 

 ing on the same substance. If we examine a fallen, 



