VINE MILDEW. 123 



their legitimate consequences as the ground of absurd hypotheses. 

 Ought we not rather to be deeply impressed with those four 

 words of the first aphorism of our common philosophic parent, 

 " Experientia fallax, judicium difficile ? " 



I regret much that I feel compelled to say all I think, 

 respecting these pretended metamorphoses. The question is not 

 respecting those which a multitude of fungals undergo, in the 

 different phases of their frequently ephemeral existence, and 

 which make them so analogous, in this respect at least, to insects. 

 But the fact is that botanists, in consequence of this natural pro- 

 pensity to estimate at a high rate their own works, and to despise 

 those of others, have with a secret complacence rested on these 

 more than hazardous assertions, in denying or impairing the 

 solidity of the principles on which the distinction of genera and 

 species is founded in mycology. In consequence, there is in their 

 opinion nothing better to do with the mass of books, in which the 

 principles of the Science are taught, than to burn them at once, 

 for they have not the courage to master them. Is it possible, I 

 would ask, to hear accusations so gratuitous and malevolent without 

 reply ? 



A far more important object is to discover what becomes of the 

 spores of the Oidiura during winter, and on what part of the 

 plant they sojourn till the following spring. The difficulty of 

 such investigation will at once appear if we consider the smallness 

 of the ovoid spore, and the still more extreme minuteness of those 

 which are contained in the pycnidia. 



Disposition to Disease. — I have exhausted what I had to say of 

 Oidium Tuckeri considered as the cause of disease ; I have still 

 to speak of the greater and less disposition to disease of certain 

 kinds of vine. The subject, however, is so extensive, and the 

 materials so abundant, that I must confine myself to a mere 

 summary. Those who desire more circumstantial details cannot 

 do better than consult the important work just published by my 

 friend and colleague, M. Bouchardat, in the Supplement to the 

 Memoirs of the Imperial Society of Agriculture for 1852, which 

 contains also a very exact chronological calendar of all the works 

 hitherto published on the subject. The following information is 

 taken from it : — 



All other things being equal, the grapes which have the finest 

 and most delicate skin, and the most succulent fruit, have been 

 the 'most seriously affected, while those with a hard flesh and a 

 thick resistant skin have been comparatively spared. At the 



