4o6 General Botany- 



organic acids. The germination of all fungus spores takes place 

 only in the presence of moisture and oxygen and at suitable tem- 

 peratures. 



Distribution of fungi. Many fungi are world-wide in their 

 distribution. Others, however, have rather definite temperature 

 requirements which limit their development to certain regions 

 and to certain seasons of the year. If the spores cannot with- 

 stand freezing temperatures, the fungus will not thrive in cold 

 temperate and arctic regions. If the vegetative development 

 requires warm temperatures, the fungus may be suppressed by low 

 temperature even when the spores are present in abundance. 

 The efficiency of cold-storage houses and refrigerators in con- 

 serving foods depends in large part upon the temperature require- 

 ments of the fungi and bacteria. 



Groups of fungi. Of the nearly 50,000 described species of 

 fungi, there are three conspicuous groups, commonly known as 

 the Tube fungi, the Sac fungi, and the Basidium fungi. 



The Tube fungi (Phycomycetes) receive their name from the fact 

 that the hyphae are for the most part tubular and without cross- 

 walls. They include the molds, water molds, and downy mildews. 



The name of the Sac fungi {Ascomycetes) is derived from the 

 peculiar way in which the spores are produced. There are 

 usually two, four, or eight spores formed inside a sac-like body. 

 To this group belong the yeasts, the powdery mildews, most of 

 the lichens, and certain of the fleshy fungi. 



In the Basidium fungi (Basidiomycetes) spores are produced 

 usually four or two in number on the end of a club-shaped hypha, 

 which is called a basidium from the Latin word for club. In 

 this division of the fungi are the smuts, rusts, and most of the 

 fleshy fungi, such as puffballs and toadstools. 



THE TUBE FUNGI OR PHYCOMYCETES 



Among the commonest examples of the tube fungi are the bread 

 molds and water molds. These molds are usually white, filamen- 



