52 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



vacuolated, and in cells which have reached maturity fre- 

 quently the protoplasm containing the nucleus occupies 

 but a small portion of the cell volume, being reduced to a 

 comparatively thin layer just inside the cell wall. Gran- 

 ules of various kinds, including metachromatic granules, 

 globules of fat and of glycogen may develop. Apparently 

 these products may function as reserve food materials. 



Mold Growth. — Most molds increase in size by growth at 

 the tip of the hyphae. Any cells lying back of the tip that 

 start to grow develop into branches. Such growth is 

 termed apical. A few molds are known in which all cells 

 may continue to grow in length and divide. Such growth 

 is termed intercalary. In apical growth the tip cell only 

 divides, while in intercalary growth cells throughout the 

 filament may divide. 



Multiplication in Molds. — Practically all molds multiply 

 by means of specialized cells termed spores. In many in- 

 stances these spores are numerous and well adapted to carry 

 the organism over unfavorable conditions and to facilitate 

 its distribution. 



A single species of mold may produce several kinds of 

 spores. A few molds have relatively complex life histories, 

 producing a different type of spore at each stage in de- 

 velopment. In general the spores developed belong to 

 two types, those which are asexual in origin and those which 

 are sexual. The asexual spore may be defined as one which 

 is not the result of the fusion of two sex cells or gametes. 



Practically all of the common types of molds produce 

 asexual spores, some several kinds. A smaller number of 

 molds produce also sexual spores. From the standpoint of 

 the botanist who is seeking to determine true interrelation- 

 ships, the sexual* spores are of great interest. From the 

 standpoint, however, of the practical worker it is possible 

 to differentiate the molds satisfactorily by observing the 

 types of asexual spores produced. 



