Studies on the Downy Mildew of Onions 



19 



hyphae with numerous long and branched haustoria penetrating the 

 cells. The mycelium itself was always intercellular, but the size and 

 number of haustoria sometimes gave the appearance of the fungus being 

 intracellular. The mycelium was irregular in width, depending largely 

 on the size of the intercellular spaces through which it was passing. 

 The fungus was easily traced from the pedicel into the receptacle, 

 where it branched in all directions and progressed toward all of the 

 flower organs. Long, straight hyphae ran the entire length of the petals 

 (figure 3), and haustoria were extended into many of the cells. The 

 mycelium was traceable from the receptacle into the stamens, where it 

 could be followed through the filament into the anthers (figure 4). All 

 parts of the anthers were invaded, with the exception of the pollen 

 cavity. The mycelium was especially abundant in all parts of the ovary. 

 The most significant fact in relation to the mycelial invasion of the 



Figure 4. section of an anther of an infected onion flower, showing the 

 presence of the mycelium of the fungus 



