The Fungi— Molds 363 



DISTRIBUTION IN NATURE 



Molds are widely distributed in soil, water, air, and in more 

 limited numbers in plant and animal tissues. Their light repro- 

 ductive spores may be carried by air currents to points some dis- 

 tance from where the mold plant produced them. If conditions 

 are favorable, these spores germinate and produce a new plant, 

 which in turn forms many additional fruiting bodies. While these 

 spores are usually not as resistant as the spores produced by bac- 

 teria, they are, nevertheless, capable of remaining dormant for ex- 

 tended periods of time under conditions relatively unfavorable for 

 most vegetative cells. In time, however, mold spores will die un- 

 less they have an opportunity to germinate. 



ECONOMIC IMPORTANCE 



Molds influence their environment both physically and chem- 

 ically. A few of these considerations will be briefly mentioned. 



SOIL FERTILITY 



There are certain preprequisites which must be fulfilled before 

 a medium can be considered as favorable for the growth and multi- 

 plication of molds. While their demands generally are not as 

 stringent as those required for bacteria, the factors of pH, moistm-e, 

 available foods, etc., are still of importance. The optimum pH for 

 the cultivation of molds lies within the range of 4.5 to 5.5, but when 

 attempting to cultivate molds on laboratory media to the exclusion 

 of bacteria and other microorganisms, the medium may be ad- 

 justed to a pH as low as 4.0. As the acidity decreases (the pH 

 increases), bacteria and actinomyces increase in numbers more rap- 

 idly than fungi. Moisture requirements are much less for fungi 

 than for bacteria. 



Molds help to stabilize the soil both chemically and physically. 

 Mycelial threads tend to entangle soil particles and to form stable 

 aggregates of soil substance. Free nitrates in soils may be assim- 

 ilated by fungi, and when these plants die, the nitrates become 

 available for use by higher plants and by other microorganisms 



