238 



INTRODUCTION TO BOTANY 



has become a large, spherical body. Meanwhile the transverse 

 wall has extended into the spherical sporangium, thus produc- 

 ing a little column (the columella), upon which the sporangium 

 contents rest. The protoplasm of the sporangium divides into 

 many small spores, which, when the sporangium wall breaks, 

 are scattered widely into the air. The musty odor which is 



detected when we smell 

 mold may be due to the 

 presence of large num- 

 bers of these spores or 

 to gases that have been 

 produced within the 

 nutrient material. 



If bread that has not 

 been exposed to the 

 air is cut in a room in 

 which the air is quiet, 

 and if one piece is cov- 

 ered directly in a glass 

 dish, another similarly 

 covered after five min- 

 utes' exposure to the 

 air of the room, and 

 another after five min- 

 utes" exposure on the 

 outside window sill, an 

 interesting test of the 

 abundance of spores in the atmosphere will be afforded. One 

 class of students, in performing this experiment, secured the 

 development of mold upon all three pieces of bread, having 

 in all five kinds of mold. Another class used sterilized gelatin 

 culture material and exposed it to the air of a schoolhouse 

 hallway for five minutes, and during the following week there 

 grew upon the gelatin eight different kinds of molds and 

 bacteria. Juices of fruits, as prunes, are also good nutrient 

 materials for experiments in growing molds. 



FIG. 185. Grape leaf with grape mildew 



A leaf of the grape, upon which may be seen the 



white, fluffy patches of grape mildew. Photograph 



by H. H. Whetzel 



