SPORE GERMINATION 357 



hanging-drop technique, 7°C. in exposed drops of water, and 4°C. in 

 prune decoction. This may serve to exphiin, in part, the differences in 

 cardinal temperatures reported by different authors. 



The method of spore germination may be determined by temperature. 

 Below 20°C. the sporangia of Phytophthora infestans germinate more 

 frequently by the formation of zoospores, while above this temperature 

 production of a germ tube is more common. 



The optimum temperatures for germination for the various species of 

 Myxomycetes were from 22 to 30°C., with an over-all range of 2 to 36°C. 

 Certain species had narrower ranges. Below 10 and above 30°C. the 

 rate of germination was greatly reduced. When the spores of Enteridium 

 rozeanum were held for a time at a temperature above maximum and then 

 returned to optimum, the spores germinated explosively through a thin 

 area in the wall (Smart, 1937). Under uniform optimum temperature 

 an irregular pore was formed and the protoplast slowly squeezed out. 



It must be emphasized that temperature affects the time required for 

 germination, as well as the percentage of germination and the growth 

 rate of the germ tubes. All three have been used as measurements of 

 spore germination. It seems likely that temperature might have a 

 greater effect upon the time of germination than upon the percentage 

 of germination. 



Heat treatment and breaking of dormancy. The effectiveness of pre- 

 heating ascospores of Neurospora tetrasperma in breaking their dormancy 

 has been discussed by several authors. Heating the spores to 50°C. for 

 a few minutes induced germination 2 or 3 hr. after they were returned to 

 a favorable temperature. Goddard (1935) found that spores thus 

 "activated" could be "inactivated" (returned to the dormant condition) 

 by placing them under anaerobic conditions for a short time. They 

 remained dormant when brought back into air. The respiration rate of 

 the activated spores was greatly increased and germination occurred 

 only after 2 to 3 hr. of continuous high respiration. Further work by 

 Goddard and Smith (1938) led to the conclusion that the heat activated 

 carboxylase, which is latent in the dormant spores, and that two different 

 respiratory systems are in operation : one, the dormant system, functions 

 in the absence of carboxylase; and the second, the active system, functions 

 after the spores are heated. Similar stimulation of germination of 

 Ascoholus ascospores by heat was found by Dodge (1912). Only a few 

 spores germinated in water without being preheated. Heating the spores 

 to 65 to 75°C. for approximately 15 min. and then returning them to 

 favorable temperature allowed good germination of most species. 



Moisture. The spores of many species of fungi will not germinate 

 unless they are in contact with liquid water. Others are capable of 

 germination on dry surfaces in an atmosphere of high humidity, usually 



