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 
Fig. 185. Grape leaf with grape mildew another after five min- 
A leaf of the grape, upon which may be seen the utes’ exposure on the 
white, fluffy patches of grape mildew. Photograph oytgide window sill, an 
by H. H. Whetzel ‘ 
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. 
