322 Journal of Agricultural Research voi.xiii.no. 6 



six weeks. At the end of this time the growth in the cultures at the two 

 extremes, 2° and 29°, was barely perceptible. The best growth was made 

 at temperatures between 16° and 25°, although at the lower temperature 

 it was somewhat retarded. Between 2° and 16° there was a remarkably 

 regular retardation of growth in proportion to the lowered temperature. 



GERMINATION OF ASCOSPORES 



Three tests of the time required for the germination of ascospores at 

 different temperatures have been made. As a result of preliminary trials, 

 the following method of making germination tests has been found the 

 most satisfactory. The leaf fragment or culture bearing apothecia which 

 are discharging spores is placed in the cover of a petri dish in which a 

 thin layer of 2 per cent water agar has been placed. Since the act of 

 transferring the culture to the petri dish often affects the rate of discharge 

 of ascospores for a time, at least 12 hours should be allowed to elapse 

 before spores are taken for germination test. Then the cover of the 

 dish is turned so that the spores fall in a new place. When a sufficient 

 number of spores have collected (from one to three hours will be required) , 

 the area on which the spores are collected is marked with a wax pencil, 

 and the cover is transferred to another dish of agar if more test plates are 

 needed. The plate on which the spores have been collected is then placed 

 at the desired temperature. The spores can easily be observed through 

 the bottom of the plate under the low power of the microscope. 



This method is open to the objection that some of the spores are exposed 

 on the plate for one or more hours at room temperature before they are 

 placed at the desired temperature. This would be a serious matter if 

 the spores germinated quickly; but since nearly 12 hours are required 

 for complete germination, it does not appear to be a large factor. 



The results of the tests are compiled in Table I. At almost all of the 

 temperatures used at least three trials have been made with spores from 

 different cultures. The results of the trials have not been divergent out- 

 side the limits of error incidental to such tests. In Table I the numbers 

 in the columns under the length of time during which the spores had 

 been kept at the given temperature represent the length of the germ 

 tube at that time in relation to the greatest diameter of the spore. This 

 number is obtained by estimate, and not by measure. In making the 

 estimate after the longer periods of time, the shorter germ tubes which 

 have apparently ceased growth are disregarded, and only the length of 

 the longer ones is considered. It may be added here that at the extremes 

 of temperature, where germination does not proceed far, the percentage 

 of germination is also greatly reduced. 



From this table it appears that the optimum temperature for spore 

 germination is between 12° and 26° C. 



