XXXIV.] 



LETTUCE MILDEW. 



273 



a common one in text books that P. ganglioniform'te, Berk., 

 does not produce oospores in lettuces, or P. infestans, 

 Mont., oospores in the potato. Our experience has been 

 the reverse of this. 



Peronospora ganglioniformis, Berk., grows on various 

 other living composite plants in addition to the garden 

 lettuce, Lactuca saliva, L., and L. altissima, M.B. Of 

 these the different sorts of sow-thistles, as the corn sow- 

 thistle, Sonchus arvensis, L. ? are most often attacked ; then 



X'4-OO 



FIG. 126. 



Oospores or resting-spores of the fungus of Lettuce Mildew, Peronospora 

 ganglioniformis, Berk. Enlarged 400 diameters. 



Garduus arvensis, Curt. ; Cichorium Endivia, L.; the 

 nipplewort, Lapsana communis, L. ; groundsel, Senecio 

 vulgaris, L.; and other plants, both wild and cultivated. 

 Weeds act as nurses of the fungus for the garden 

 lettuce. 



For the prevention of the disease it is desirable that no 

 decaying lettuces or weeds belonging to the series just 

 mentioned be allowed to rot in the fields or kitchen 

 T 



