THE ARTIFICIAL PRODUCTION OF SPORES. 



169 



perature of i C. for five to seven days, the protoplasmic 

 contents of the resting cells break up into small spherical spores, 

 from two or three to twenty-five in each cell. In most cases 

 these spores are discharged from the resting cells as soon as they 

 are formed. They have thick cell walls and are non-motile. 

 They may be kept indefinitely at any temperature below 8 C. 

 and withstand desiccation perfectly. 



When the spores are removed to the temperature of the. room 

 and isolated in small closed cells under the microscope their de- 

 velopment into the motile Monad can be easily followed. The 

 first attempts to demonstrate the development of the spores 

 failed in several instances because of a lack of oxygen in the 

 closed cells in which the spores were isolated, due to the 

 presence of motile Monads which originated from resting cells 

 isolated with the spores. But finally, at Dr. Loeb's suggestion, 

 some fresh-water algae were mixed with the spores as soon as 

 they were returned to the temperature of the room. In this way 

 a supply of oxygen was maintained, and the development of the 

 spores began at once. The first change that can be observed is 

 the appearance of a thin layer of protoplasm which grows out 

 of the spore. This protoplasmic layer develops into a small 

 spherical cell, which gradually becomes separated from the 



FIG. 4. Four stages in the development of the spore into the motile Monas. 



spores. The cell at first is hardly visible because of the extreme 

 transparency of its protoplasm, but it eventually becomes 

 granular and develops a flagellum, which appears to originate 

 as a long pseudopod extending outward from the protoplasm. 

 The Monad formed in this way finally becomes motile and 



