8 



Minnesota Plant Diseases, 



a characteristic structure and method of growth. This myce- 

 lium is composed of fine microscopic threads, more or less 

 branched and densely interwoven to form loose, woolly masses, 

 as in bread mold, or may even be compacted to form solid 

 bodies. All fungi reproduce in some form by means of micro- 

 scopic cells, more or less spherical in shape, and often as small 

 as 1/2000 of a millimeter in diameter. They are usually, how- 

 ever, larger. These tiny cells are known as spores and have 

 various forms and methods of production, which are character- 



FIG. 1. The mycelium of a food-mold fungus (Penicillium). A. Mycelium which is 

 entirely absorptive and tufts (t) of spores (reproductive tract). The original spore 

 from which the mycelium grew is seen at a. B. Highly magnified view of spore tuft. 

 After Zopf. 



istic for different groups of fungi. There is, however, no spore 

 form or spore receptacle which is common to all fungi, nor are 

 spores themselves confined to fungus plants. 



Plants as well as animals can usually be best understood by 

 their ancestry. The fungi have all descended from the algae, 

 probably not, however, from one, but from several groups, e. g.. 



