288 
BRAMBLES AND BAY LEAVES. 
true cause had been hinted at again and again by the 
poets—whose words are as often prophetic, in regard to 
the discoveries of science, as they are of ethical and his¬ 
torical developments. Shakspere, in the passage already 
quoted, sounds the key-note where he speaks of the 
fairies as “ making the midnight mushrooms;” and the 
author of “ Round about our Coal Fire” speaks sugges¬ 
tively of the frequent appearance of these rings in spots 
“ where mushrooms grow ;” these luxurious rings of grass 
being caused solely by the growth of successive crops of 
certain species of fungi. 
That law of agriculture which insists upon the rotation 
of crops has no more palpable illustration than these 
mysterious developments in the meadows. The recent 
discovery, that when one kind of plant has occupied a 
spot for a certain length of time the soil becomes unfit 
for that plant, but will readily nourish another kind, 
makes it evident that rotation of crops is no invention of 
man, but a provision of nature, and a prominent feature 
in her vegetable economy. Dr. Roget, in his Bridgewater 
treatise on “Animal and Vegetable Economy,” gives 
the result of a series of experiments performed on plants, 
by immersing their roots in filtered water for several 
days; when, after the lapse of a certain time, the water 
became charged with certain excretions, or matters cast 
off from the plant; which excretions, in the case of the 
roots of the Chandenilla muralis , consisted of a bitter 
narcotic substance, similar to opium. M. Macaire found 
that neither the roots nor stems of the same plants, when 
completely detached and immersed, would produce this 
effect; and hence he concludes that it is an exudation 
