DEPARTMENT OF EXPERIMENTAL EVOLUTION. 105 



within which was placed an inoculating box — all of which were sterilized 

 before using — reduced contamination during inoculation to a minimum, 

 as shown by the presence or absence of growths in Petri-dish cultures kept 

 exposed while all inoculations were in progress. A record of two hours' 

 inoculating, followed the next day by one hour's inoculating, without a 

 single viable germ falling upon an exposed Petri dish 10 cm, in diameter, 

 shows the value of the precautions taken. Contamination is likely to 

 occur in Petri dishes after inoculation, and, to avoid this, ''roll tubes" were 

 devised from 0.5 gallon cylindrical specimen jars and were used throughout 

 the investigation whenever "separation cultures" were made to obtain 

 growths from individual spores. A note on this new method of separation 

 cultures is being prepared for the journal "Phytopathology." 



The preliminary work in formulating a standard medium and in devising 

 means to prevent infection from outside sources has consumed considerable 

 time, but has been necessary to insure accurate and credible results. 



Before testing the influence of external stimuli upon the possible forma- 

 tion of mutations, all of my 24 mated dioecious species as well as 10 her- 

 maphroditic forms (a total of 58 cultures) were separated out, so that each 

 strain investigated could have a single spore as its origin. A preliminary 

 investigation of the growths resulting from single spores of these forms 

 showed that species in particular — an hermaphroditic form — that gave 

 such a relatively great variability in its progeny that it has received most 

 attention. I have cultures of this species from four different localities and 

 have examined separately the growths from individual spores to the num- 

 bers indicated from the following sources: 



Cambridge, Massachusetts 13,740 



Geneva, Switzerland ; . . . . 1,925 



Daytona, Florida 364 



Waverly, Massachusetts 6,943 



Total colonies examined 22,971 



Of these 22,000 and more individual colonies examined, those that seemed 

 different in appearance from the normal type have been isolated to the 

 number of some 25 or 30. Among the aberrant characters observed are 

 absence and increase or decrease of zygospore production, peculiarities in 

 color, density, and rapidity of mycelial growth, differences in height of 

 sporangial filaments, the almost exclusive production of yeast-like cells 

 in place of a filamentous mycelium, and the production of a filamentous 

 mycelial growth devoid of sporangia. Some of these variants are surely 

 temporary conditions, for they eventually tend to revert to the normal 

 type. Others may be more permanent, but have not been sufficiently 

 investigated. All, however, tend, partially at least, to reproduce the new 

 characters and some have for several sporangial generations kept their 

 pecuharities in gross cultures during the few months it has been possible 

 to propagate them. Many of them would undoubtedly be described as 

 distinct species by specialists in the group. Of these and other molds, 

 several hundred test-tube cultures have been made up with nutrient, to 

 which various poisonous chemicals have been added, but time has not yet 

 admitted a test of the effect of these chemical stimuli on the offspring. 

 Enough has been done, however, to show the extreme lability of at least 

 a single species under normal conditions of cultivation. 



