CLASSIFICATION OF THE MOLDS 57 



celled spores may be elongate or even spindle-shaped, cylin- 

 drical, or club-shaped. Two-celled spores occur in many 

 species of molds. Others produce elongate spores, having 

 several or many cross walls. The spores of some molds are 

 many-celled, the walls being not oiily transverse but longi- 

 tudinal or irregularly disposed. The spores of some molds 

 branch, in others they are curved, sometimes being coiled 

 like a spring. 



Spores are usually adapted to wind distribution, being 

 caught up by air currents and carried to considerable dis- 

 tances. They are, therefore, commonly present in the air 

 and are constantly observed in the laboratory. When they 

 are brought under favorable conditions for growth, they 

 germinate, developing a mycelium. 



Classification of the Molds 



It has already been noted that the term mold as used in 

 bacteriology is not recognized in this exact sense by the 

 botanist. The molds are plants belonging to several dif- 

 ferent groups of fungi. They are all alike, however, in 

 possessing a much-branched mycelium and growing as a 

 velvety or cottony mass upon ordinary culture media, or 

 upon decaying materials. 



Many different kinds of molds are known, in fact, more 

 than a hundred different genera have been described. Of 

 these, however, comparatively few are common, and the 

 student should readily recognize nine tenths of the molds 

 with which he may come in contact by comparatively sim- 

 ple microscopic examination. In many cases the genus to 

 which the mold belongs can be determined by its general 

 appearance. Some of these common genera have many 

 species. In the following account a description will be 

 given of the commonest of the genera together with notes 

 on methods of differentiating some of the species. 



