Minnesota Plant Diseases. 



FIG. 171. Downy mildew of melons and cucumbers. 1. A spore-bearing thread; sp. young 

 spores; 2, 2' and 2", mature spores of the ordinary form. 3. Spore-bearing thread 

 emerging from an air-pore on a leaf. 4. A cluster of spore-bearing threads taken from 

 a cucumber leaf in dry weather, t, unusual types of spore-bearing threads and spores. 

 6. A short stalked spore from a muskmelon leaf. 7. Cells of a cucumber leaf with the 

 fungus mycelium between them; sucker threads h, h' and h". 8. An unusual type of 

 spore from the cucumber. 9. A very large pear-shaped spore of unusual occurrence. 

 Highly magnified. 7. After Humphrey; all of the others after F. C. Stewart. 



