DEVELOPMENT OF PLANTS 



213 



to float ofif in the air as an invisible dust. The spores will germi- 

 nate at once and produce a new plant under suitable conditions 

 of moisture and food, or they will retain their vitality for months 

 if kept dry. As the spores are disseminated, the dome-like struc- 



FlG. 135. A, B, early stages in the development of the sporangium of 

 Rhizopus. C, the formation of the vacuoles which separate the denser peri- 

 pheral protoplasm from the more watery central region. D, the vacuoles 

 are flattening out and the denser protoplasm is becoming separated into 

 multinucleate segments, E, the multinucleate segments are rounding off to 

 form the spores and a wall has formed over the columella. F, the sporan- 

 gium has ruptured, permitting the scattering of the spores and the columella 

 has formed an umbrella-like structure owing to the loss of its watery con- 

 tents. — After Swingle. 



Fig. 136. Sexual reproduction in the black mould: A, the meeting of 

 the tips of two hyphae.J B, later stage, the lower part of the figure shows 

 the cutting off of the tips by transver.se walls and in the upper part of the 

 figure the fusion of the_^'contents of the two gametangia thus formed has be- 

 gun. C, mature gametospore. 



