1921] BLAKESLEE, CARTLEDGE, & WELCH—CUNNINGHAMELLA 213 
interest, whoever, centers upon the grades inclosed in paren- 
theses, which indicate reactions which have changed from a 
perfect to an imperfect reaction as shown by the production of 
stages resembling imperfect hybrids in place of zygospores. It 
will be seen that there are certain unexplained irregularities in the 
production of zygospores or of only imperfect reactions which 
indicate that the preliminary tests have not discovered all the 
factors involved. Enough has been learned, it is believed, to 
indicate that some of the factors are environmental which deter- 
mine whether a sexual process in this species goes through to 
TABLE VII 
RETESTS _ CONTRASTS BETWEEN RACES OF Cunninghamella bertholletiae: CAPITAL 
RS INDICATE GRADES OF ZYGOSPORE FORMATION; SMALL LETTERS INDICATE 
pri bees OF IMPERFECT SEXUAL REACTION; LETTERS INCLOSED IN PARENTHESES 
SHOW CHANGE IN TYPE OF REACTION FROM ZYGOSPORE FORMATION TO IMPERFECT 
REACTIONS; REACTIONS WITH ASTERISK INDICATE PRESENCE OF PARTHENO- 
SPORES; NO. 230 NUTRIENT USED 
Races | 266 | 729 | 732 | 457 | 737 | 213 | 450 | 731 | 219 | 180 | 241 | 232 | 460 | 718 | 74x | 721 
FSG ot alt tO) ec © eel ee ee 
iy totes (aR RN GR ee a C1 eas OA Bes ae 
AOC ie | ee re arte Oy Oe) + 
Lege A oo Deuie MPC Gt Ge Aa) ee Ske ns ies Gey ie ate 
completion with the formation of zygospores or is confined to the 
first reaction with the formation of progametes or at the most 
gametes. 
Although environmental differences not readily controlled in 
the cultures may have some influence upon the extent of the sexual 
reaction, the genetic constitution of the individual races in the 
main must be responsible for their sexual behavior. We have not 
succeeded, however, in an attempt to subject the genetic differ- 
ences to a factorial interpretation. Distinct classes of plus and 
minus races differing sharply in the strength of their sexual activity 
or in their capacity to form zygospores or only imperfect reactions 
with certain other races do not seem to exist. Thus certain con- 
trasts from table VII A may be arranged in such a way that no 
