58 PARASITES BELONGING TO THE GENUS GLOMERELLA. 



leaves had developed acervuli of Glomerella and some showed peri- 

 thecia as well. 



From these and numerous other experiments of a similar kind per- 

 formed at different times during the year with leaves from other 

 plants, it appears that this fungus is quite generally present in the 

 leaves of many plants in a dormant or innocuous condition awaiting 

 some weakening of the host or other favorable condition which may 

 give it an opportunity to develop. 



PEDIGREED CULTURES OF GLOMERELLA CINGULATA FROM 



AVOCADO. 



The characters compared in the pure-line cultures were chiefly the 

 relative abundance and particular characteristics of the conidial and 

 perithecial fructifications. These were all perithecium-producing 

 strains at the start. In some cultures conidia predominated and 

 but few perithecia occurred; in others conidia were few and perithecia 

 predominated. In some the conidia were scattered and hyphomyce- 

 tous, while in others they were produced in distinct acervuli, fre- 

 quently large. The perithecia were sometimes separate and scattered 

 evenly and thickly over the surface of the medium; in other instances 

 they were aggregated in dense masses. 



The arrangement of the perithecia, whether separate or aggregated 

 in a stroma, has usually been regarded by mycologists as important 

 and has been used as the basis for separating genera and families. 

 All the cultures were grown on the same medium (corn-meal agar) 

 in a culture room under ordinary room temperature and conditions. 



FIRST SERIES OF SEVEN GENERATIONS STARTED FROM A SINGLE 



ASCOSPORE. 



Generations 1 and 2 were very similar in appearance. They pro- 

 duced conidia and an abundance of perithecia evenly scattered over 

 the surface of the medium, as shown in tube 2a, Plate VIII. Gen- 

 eration 1 also showed some submerged perithecia. 



The third generation was very similar to the first two but showed 

 more of the deeply submerged perithecia. 



In the fourth generation the perithecia, instead of being scattered 

 evenly over the surface, as in the three previous generations, were 

 compacted in black masses, giving the cultures a very different 

 appearance from the earlier generations. 



Generations 5, 6, and 7 showed the same characters as generation 4. 

 The variation in arrangement and grouping of the perithecia seems to 

 have been transmitted from generation 4 through these three genera- 

 tions. This series was discontinued at this point. In this case an 

 important variation or mutation suddenly occurred in the fourth 

 generation and was transmitted through three following generations. 



252 



