Lecture on the Parasitic Fungi of the British Farm. 393 



Fig. 14 shows the microscopic appearance. This fungus is, 

 I believe, new to Europe ; so widely distributed a species 



14. Botrytis infestans. 



could not have been overlooked. This diagram is the same 

 as that given by Mr. Berkeley in his admirable paper on the 

 potato fungus. The mycelium may be observed traversing the 

 cellular tissue of the leaf, and one of the threads of botrytis, 

 that to the left, issuing from a stoma. Mr. Berkeley, the very 

 highest authority, is of this opinion ; and he 

 writes me word, " I am convinced more and 

 more that the fungus is the real enemy." Cer- 

 tainly, all other theories have failed. The prin- 

 ciples of the geographical distribution of food- 

 plants plainly show us that extremely minute 

 and inappreciable differences in climateric con- 

 dition may throw plants into an unhealthy state ; y 

 which conditions might exist unsuspected for a j 

 few years. Hereby plants may be brought jf 

 into a state which renders them capable of | 

 being attacked by certain parasitic fungi, of 

 which the potato blight may be an example, 

 and the botrytis infestans become, as it really 

 seems to be, the proximate cause of the malady. 

 The botrytis is found on the tubers ; but besides 

 this &fusarium, which must not be confounded 

 with the former, nor regarded as characteristic 

 of the potato disease, but of another, often 

 occurring in the same tuber with it. (See 

 Fig. 15.) This fusarium, highly magnified, is 

 represented in this figure. It will be per- 

 ceived to be totally different from the botrytis, 

 and the spindle-shaped spores tell the origin 

 of its designation. Genuine science alone Fig 

 enables us to make such discriminations ; and the tuber of Potato, 



