PHYSIOLOGICAL CONDITIONS OF SPORULATION 119 



D. Humidity. Naegeli has argued that the principal factor in 

 sporulation is desiccation and that this phenomenon is brought about 

 only in cells which are partly dried. The investigations of Hansen, 

 on the contrary, have shown that humidity is an important, if not 

 indispensable, condition of sporulation. It is easy to show this by 

 Hansen's own experiment. 



Blocks of plaster of Paris are prepared and then plunged into 

 water in order to soak them; on each of these, a little of the yeast 

 is placed and the blocks placed in dishes without water, covered with 

 a glass plate. Some other blocks are placed in dishes covered with 

 a filter paper and still containing no water. Another series of blocks 

 are placed in dishes with water and covered with a glass plate. In 

 a few days it will be seen that the yeasts in the dishes with water 

 have formed numerous ascospores; those in dishes without water and 

 covered with the glass plate have a few; those in the dishes covered 

 by a filter paper have still less. 



The evaporation of water hindered the formation of ascospores. 

 Humidity is then necessary for sporulation. Evaporation does not 

 completely stop the formation of spores, for a few cells will sporulate 

 on the blocks undergoing evaporation. Thus, we are able to explain 

 sporulation in yeasts in nature on fruits; in the superficial layers of 

 the soil they are capable of sporulating in spite of the absence of 

 humidity. 



E. Light. According to the investigations of Purvis and Warwick 1 

 the rays of certain wave lengths have an influence on sporulation. 

 By placing moist plaster of Paris blocks in dishes, the walls of which 

 were covered with different colors, they were able to establish the 

 following facts: 



1. The red rays of longer wave length accelerate the formation 

 of ascospores which appear more rapidly than in the presence of white 

 light. They also seem to be more favorable to sporulation than ob- 

 scurity and seem to stimulate sporulation. 



2. The green rays seem to retard the formation of ascospores. 



3. The blue or violet rays retard sporulation more effectively 

 than the green. 



4. Finally, the ultra-violet rays have a pronounced retarding 

 action; they seem to have a bad effect on the vitality of the cells. 



These results are able to be explained on a chemical basis, for it is 

 well known that the rays of short wave length have a greater chemical 

 activity than the long wave lengths. Also it might be regarded 

 that the former determine the chemical modifications in the cell which 



1 Purvis, E. and Warwick, R. The influence of spectral colors on the sporu- 

 lation of Saccharomyces. Proceedings of the Cambridge Society, 14, 1907. 



