OF THE FUNGI. 39 



mense contributions to our STORE OF FACTS, not only pre- 

 pare us for such a theoretic step, but actually, by pregnant 

 allusions, lead the way. It is, then, not so much -a rash 

 generalization, in advance of the opinion and knowledge 

 of the age, as a very natural result of that knowledge 

 collected and classified. It is an expression, if not of the 

 sentiment, at least of the science of the present era. 



Under this impression, I undertake the adventurous 

 duty of developing a theoretic result, not expecting to do 

 more than obtain for it, at present, a hearing and an ex- 

 amination, since its demonstration, if ever completed, 

 must exact, for years, the enlightened and patient toils of 

 many philosophers. " There never is," says Bischoff, 

 "an important and comprehensive discovery made at once; 

 the elements of it are generally obtained from different 

 quarters, and from all these truth at last results." 



Imitating the natural philosophers, I have constructed 

 a theory, not to be esteemed devoutly true, but as, in the 

 present state of knowledge, the most perfect explanation 

 of the known phenomena of the case; and as the least 

 exposed to the many objections easily brought against any 

 other hypothesis. 



It may be thought that the cause assigned is not ade- 

 quate to the rapid production of the effect. Can a mi- 

 nute vegetable, however distributed, contaminate the air 

 of a large marsh or field, in the course of a few minutes 

 or hours ? When we remember how minute a quantity 

 of a reproductive organic virus is, in other cases, neces- 

 sary to the infection of a proper subject, we might leave 

 the argument to that defence alone; but I think there is 

 a better one, in the wonderful growth and ready diffusion 

 of the plants to whose nocturnal potency I am inclined to 

 ascribe malarious fevers. 



