7o6 FUNGI 



by the fungus, Macrosporiu7n Solani Ell. et Mart., only conidial 

 forms of which are known. The conidia and hyphae bearing 

 them are brown. Each of the former when fully developed is 

 somewhat spindle-shaped and formed 

 of several cells as at A, Fig. 236. The 

 mycelium is colourless and penetrates 

 into the tissues of the leaves upon 

 which it usually causes small greyish- 

 brown patches, which are much 

 slower in development and paler in 

 colour than those due to Phytoph- 

 thora infestans. The disease often 

 occurs early in the season when the 

 plants are not more than 5 or 6 

 Fig. 236.-^4, Portion of hyphae inches high, especially in dry weather 



and conidiophores of a species of - . \ . . -r 



Macrospnium, showing two com- and m dry situatiODS. in Severe 



pound conidia. B, the same of a 1,11 1 



species of ^ter»ar/^ (enlarged =50 cascs, where the leavcs or large areas 

 laraeters). ^^ them are killed at an early stage 



of growth, the crop of tubers is necessarily small but is always 

 sound. 



A fungus, designated Alternaria Solani by Sorauer, and very 

 nearly related to the above Macrosporium if not identical with it, 

 has beeiKobserved to cause a leaf-disease of the potato plant in 

 many parts of Germany similar in all respects to the American 

 ' Early Blight.' 



Both these species belong to an imperfectly known group of 

 fungi which are mainly saprophytes, but which appear to be cap- 

 able of attacking plants when the latter have been previously 

 weakened or injured by excessive heat, dryness of soil and atmo- 

 sphere, and depredations of insects. The application of Bordeaux 

 mixture is found to be very beneficial in such attacks. 



Ex. 285. — Examine dead patches on the surfaces ot potato leaves with a 

 low power and search for Macrosporium or Alternaria Solani. If found, the 



