DIRECTIONS FOR LABORATORY STUDY. 375 



5. Snip off a few ripe sporangia with scissors, handling them 

 cautiously to avoid breaking or tangling them ; mount in alcohol* 

 and examine. Crush (if not already broken) and observe numer- 

 ous dust-like particles, the spores, which escape. 



6. Demonstration. Mount a full grown but immature sporan- 

 gium and show the structure of sporangium with septum grown 

 up into it forming the columella ; the spores. (^[ 316, fig. 220.) 



B. WHITE RUST [Cystopus portulacce). 



1. Demonstration. Boil a leaf of purslane for a minute or two 

 in 5^ potassic hydrate. Tease apart the tissues of leaf with 

 needles on a slide, mount and show the mycelium of the fungus, 

 consisting of tangled hyphae ramifying among the cells of leaf. 



(IF 51, 52.) 



Examine a dried leaf. Observe 



2. The white blisters [spore beds) here and there on the surface ; 

 the thin membrane (the epidermis of the leaf) by which they are 

 covered ; in older blisters the cracking and final disappearance of 

 this skin. (Tf 312, fig. 210. ) 



3. The white powdery spores which jar out or can be dislodged 

 with needle. 



4. Demonstration. Cut a transverse section through one of 

 these spore beds and show the close set ends of hyphae producing 

 the spores in chains. (IT 313.) 



5. Cut a transverse section of the leaf or stem, mount and 

 observe the numerous dark dots scattered through the tissues of 

 the host. These are the resting spores with thick opaque walls. 



6. Demonstration. Show in a similar section the spermaries 

 and ovaries, and the various stages in the maturing of the fertil- 

 ized egg into the resting spore. 



C. MILDEW (Microsphczra Friesii, or Erysiphe communis). 



Examine dried leaf bearing mildew. Observe 



1. The whitish interlacing hyphae on surface of leaf, forming 

 the mycelium. (If 50.) 



2. The distribution of the fungus ; does it cover the whole leaf 

 or only occur in patches ? Compare the earlier and later gathered 

 leaves as to this. 



* Because water will not readily wet them. Replace alcohol as it evaporates ; it does 

 so rapidly. 



