Feb. 3. 1919 Physoderma Disease of Corn I45 



GERMINATION OF THE SPORANGIA 



The more essential factors influencing sporangium germination and 

 zoospore formation are moisture, temperature, and fresh air. After the 

 sporangia have become thoroughly dried, it is very difficult to obtain 

 germination. Sporangia which have just matured germinate readily 

 when taken directly from the green corn plant. Germination was best 

 obtained by placing the sporangia in a small amount of water in a watch 

 glass or other shallow vessel, which was in turn placed in a large moist 

 chamber. The sporangia seemed to germinate equally well in either 

 distilled or tap water. The moist chamber was kept in an incubator or 

 placed in the open room where the temperature was high enough for the 

 germination of the sporangia. An incubator, in order to give good re- 

 sults, should be large and well regulated so as to keep the air as fresh 

 as possible. The moist chamber should be kept thoroughly damp and 

 should be rather large. The temperature should be kept constantly 

 between 23° and 30° C, and preferably at 28° to 29°, as this seems to be 

 the optimum range of temperature for germination. Sporangia placed 

 as nearly as possible under these conditions often fail to germinate for 

 some unknown reason. At other times sporangia from the same source 



germinate readily. 



With the proper conditions of temperature, moisture, etc., the endo- 

 sporangium absorbs water and begins a process of swelling, which causes 

 the lid or cap of the resting spores to open in doorlike fashion or to be 

 carried at the apex of the protruding endosporangium (PI. 1 3, b-d) . The 

 lids begin opening in from 30 to 48 hours after the sporangia haye been 

 placed in the incubator. The granular content of this endosporangium 

 begins rounding up into small nuclei, or oil droplets, which finally become 

 the central bodies of the zoospores. Within a few hours after the sporan- 

 gia start opening, zoospores are formed with the small oil droplets as 

 centers. A small projection, or papilla, develops at the apex of the thin- 

 walled endosporangium, and after the zoospore formation is complete a 

 movement of the contents of the endosporangium can be seen to take 

 place toward the projection, which breaks open, whereupon the zoospores 

 are liberated in rapid succession (Pi. 13, e)- These zoospores, which are 

 usually 20 to 50 in number, swim away at first with a very jerky motion, 

 which gradually becomes more uniform until their motile stage has ended. 

 This occupies from one to two hours, depending somewhat on the tempera- 

 ture to which they are subjected. With cooler temperatures their active 

 period is shorter. After their motile stage is over they settle down and in 

 most cases lose their cilia and spread slightly in an ameboid fashion 

 before germinating. The various stages of germination and zoospore 

 formation and activity were studied with the aid of the high power lens 

 of the microscope which was immersed in the zoospore suspension con- 

 tained in a watch glass. The water in this case serves very nicely as an 



