MICROSJ'ILERA 111 



3. Crush the ascocarps carefully by pressure on the cover 

 glass with the tip of a scalpel while watching them under 

 the microscope. Observe the escape of the sacs, called 

 ascl, containing spores. Note their number and form. 



4. Draw an ascus, or group of asci with the spores, ascospores. 

 What is the number of spores, their form and arrange- 

 ment ? Show these points in your drawings. The sexual 

 organs of the mildews are small and not easily studied 

 (see Frinciples, Fig. 219, and the paper by Harper, " Sex- 

 ual Keproduction and the Organization of the Nucleus in 

 Certain Mildews," Carnegie Institution of Washington, 

 Publication No. 37, 1905). 



B. The conidial fruit. Moisten with a potash solution the 

 surface of a leaf which appears powdery and scrape off the 

 mycelium. Observe the upright filaments, or conidiophores, 

 which develop terminally a chain of air spores, or conidia. 

 Other types of the mildews are frequently better for the 

 study of the conidial fructification, as, for example, ^tysipke. 



Questions. Is there mycelium of the mildew in the interior 

 of the host ? How does it obtain its nourishment ? Which 

 forms of spores, conidia or ascospores, might serve better 

 to carry the fungus over unfavorable seasons, and which to 

 multiply the plants during the growing season? Describe 

 the life history of the lilac mildew. 



112. Penicillium and Aspergillus, the green and yellow mildews. The green 

 mildew, or " mold," Penicillium., is a very common form and begins to appear 

 on bread shortly after the i)read mold has reached a luxuriant development. 

 On what other substances have you observed the green mildew growing ? 

 The yellow mildew, Aspergillus., may be obtained on cheese in a moist 

 chamber and is not uncommon on damp leather, herbarium material, and 

 other substances that " mildew.'" The fructifications of these two forms are 

 generally conidial. Describe their appearance, 



A. Conidial fructifications. Place a small quantity of the fructitication 

 on a slide in a drop of alcohol (to drive out air bubbles), followed by 

 water. Distribute the material well and mount. iStudy under the 

 highest magnification : 



