152 MICROSCOPIC FUXGI. 



on the leaves, stems, and tubers under a glass 

 sufficiently air-tight to prevent evaporation, he pro- 

 duced the brown spots^ and traced their progress 

 from the earliest stages. 



There are a few practical conclusions which may 

 be di-awn from these discoveries. In the first 

 place, it is clearly shown by the production of the 

 spots that the fungus is capable of causing the 

 disease, a fact which has been disputed, but now 

 placed beyond doubt. The inference is, that not 

 only is it capable of producing, but is really the 

 cause of the potato murrain. With bodies so 

 minute and active as the zoospores, there can no 

 longer be difficulty in accounting for their pene- 

 trating the tissues of the plant. They are most 

 active and productive in wet weather, especially 

 when it is also warm. Moisture appears to be 

 essential, and a dry season the greatest enemy to 

 the spread of the disease. That bodies so minute 

 and subtle should have baffled all efforts to destroy 

 or eradicate, is not now surprising. Whether any 

 method will be found to contend successfully with 

 it, is now more doubtful than ever. A careful 

 re-perusal of the old facts by the aid of this new 

 light will tend to the elucidation of much of the 

 mystery in which the subject has been involved. 

 All who have hitherto been sceptical of the myco- 

 logical source of one of the greatest pests of modern 

 times should study M. de Bary^s pamphlet. 



The potato mould has been judiciously named 



