18 



Harold Thurston Cook 



pedicels, and the flowers, prepared at the field laboratory with a freez- 

 ing microtome and stained with cotton blue in lactophenol or with one- 

 half per cent eosin in water, demonstrated the presence of mycelium, 

 which could be traced from the stalk up through the pedicel into the 

 base of the ovary. In some sections conidiophores were observed aris- 

 ing from the mycelium in the pedicels, thus proving the identity of the 

 fungus. The remainder of the inflorescense was fixed in chrom-acetic- 

 and picric-acid fixing solutions, dehydrated, and embedded in paraf- 

 fin for later study. Sections of this material, cut 7 microns thick and 

 stained with Haidenhain's haematoxylin, Flemming's triple, or Dela- 

 field's haematoxylin, demonstrated the extent of the floral invasion 

 by the mildew fungus. These sections showed that all of the flower 

 parts had been invaded. There was an abundance of the mycelium 

 in the pedicels (figure 2), where it consisted largely of long, straight 



Figure 3. longitudinal section or a petal of an infected onion flower, showing 



THE LONG, STRAIGHT, INTERCELLULAR HYPHAE AND THE INTRACELLULAR HAUSTORIA OF 



THE FUNGUS 



