INTRODUCTION. 3 
with a luxuriant growth of green conferve, which 
go on increasing until the water is choked up with 
vegetable matter, and becomes converted into a 
bog. How rapidly does Nature bring back into 
her own bosom the ruin which man has forsaken, 
harmonizing its haggard features with the softer 
hues and forms of the scenery around! How 
quickly does the newly-built wall, which offends 
the eye by its garishness, become, by the living 
garniture of mosses and lichens that creep over it, 
a picturesque object in the landscape! Nature, 
faithful to her own law, ‘ Be fruitful, and multiply, 
and replenish the earth, produces even in the 
hottest thermal springs special vegetable forms, 
whose structure is wonderfully adapted to their 
situation and requirements, and crimsons even the 
cold and barren surface of the arctic or alpine 
snow.with a portentous vegetation. She develops 
a strange weird frost of organic life upon the 
bark of trees, upon naked rocks, upon the roofs 
of houses, upon dead and living animal sub- 
stances, upon glass when not constantly kept 
clean, and even on iron which had been sub- 
jected to a red heat a short time before. As 
if there were not room enough for the amazing 
profusion of plant-life, she crowds her productions 
upon each other into the smallest compass, and 
makes the highest forms the supporters of the 
