THE PRODUCTION OF PERITHECIA IN GLOMERELLA. 73 



racial character which does not depend primarily on special condi- 

 tions of nutriment or environment, This conclusion does not, 

 unfortunately, bring us much nearer to the real cause of the phenome- 

 non; it merely eliminates some of the factors heretofore regarded as 

 controlling. The real nature of the inducing causes (for such must 

 be supposed to exist) which determine whether a race shall produce 

 as oogenous or only conidial fructifications is still unknown. Most 

 frequently a strain producing fertile perithecia produces them in 

 abundance. All sorts of intermediate conditions, however, occur 

 from strains which produce only sterile peritheciumlike bodies or 

 sclerotia to those which produce quite constantly great quantities of 

 fertile perithecia. It is, of course, not certain that their behavior in 

 nature corresponds in this respect to that under artificial conditions. 

 Not all of the cultures started with conidia taken from acervuli 

 which were associated with fertile perithecia on the same leaf pro- 

 duced perithecia. There is no certainty, however, that the acervuli 

 and perithecia arose from the same strain, as the manner of the 

 development of the fungus on leaves in moist chamber appears in 

 many cases to indicate that there are more or less numerous points 

 of dormant infection from which the fungus develops and the growth 

 from these finally covers the whole leaf, as shown in Plate V. The 

 intermingling of fructifications originating from different infections 

 perhaps explains why no perithecia were produced in a number of 

 cases in which cultures were made from leaves showing both acervuli 

 and perithecia more or less mixed. No ascogenous strain has ever 

 appeared in any of the hundreds of cultures of conidial strains which 

 have been grown under various conditions on different substrata. 

 Not having had an opportunity to observe the transition from a 

 nonascogenous to an ascogenous race, any attempt to account for 

 this change, which apparently must occur, would be purely hypotheti- 

 cal. The existence of certain intermediate conditions might suggest 

 the gradual development of these ascogenous races, while the failure 

 to produce any evidence that cultural or other environmental influ- 

 ences determine their production seems to indicate a deeper and more 

 obscure cause for their origin. Ascogenous strains may perhaps 

 arise as mutations. This suggestion, however, throws no light upon 

 the cause of their origin. 



It is possible that a knowledge of the nuclear phenomena occurring 

 during the stages of development preceding ascus formation may 

 throw some light upon this problem. The possibility of the existence 

 of plus and minus strains uniting as in Mucor has been considered. 

 In many cases where colonies originating from separate ascospores 

 or conidia of perithecial strains meet in a plate culture there is a 

 greater development of perithecia along the line of contact than in 



252 



