BASIS FOB SPECIFIC CHARACTERIZATION. 13 



by a species in a particular environment. Th« v correlative question 

 whether the characters of a given species of mold can be perma- 

 nently changed by passing through a series of cultures upon different 

 media is involved in the same investigation. It is asserted by some 



workers that the physiological react ions of molds (if not also the 

 morphology) can be changed, and that such changes persisl after 

 the return of the species to the original environment. So far as this 

 investigation has gone such a view is certainly not supported by the 

 conduct of the species of P< niciUium which have hen studied. In 

 those species most thoroughly studied both the physiological and 

 morphological reactions have appeared to be very reliable. A sum- 

 mary of these observations follows: 



1. The same species may differ greatly in morphology and physi- 

 ological reactions when grown upon different media. 



2. Two species closely similar, when grown parallel in one en- 

 vironment, may differ characteristically when transferred to a differ- 

 ent medium or a different set of conditions. 



3. With these species the repetition of culture under particular 

 conditions produces fairly constant morphology and reactions. 



Forms arising in this way have been designated as ecads by Clem- 

 ents^ in a recent discussion of the "Aspects of the species question." 

 This name is used preferably for forms whose origin is known either 

 because produced by cultivation or under such carefully determined 

 natural conditions as admit of full description. With species of 

 this genus in which part at least of the morphological characters of 

 every culture are definitely attributable to the conditions and to the 

 chemical character of the substratum, practically all known forms 

 would therefore be properly designated as such ecads. If described 

 as ecads, however, each description must be limited strictly to the 

 data obtainable upon a single medium, whereas by writing into the 

 description the reference to media it has been found possible to in- 

 clude a much more complete set of characters than would readily be 

 worked out from a single set of conditions. 



These observations lead to the conclusion that the cultural descrip- 

 tion of species of molds demands the recognition of the points noted 

 below: 



1. The culture media and conditions must he described SO fully as 

 to make the repetition of the culture upon t he same medium and under 

 approximately the same conditions easily possible anvw here. 



2. The habit, .structure, and appearance of the colony must he 

 given as it develops upon at least two standard media of decidedly 



different composition. 



3. The physiological effects of the colony upon these media should 

 be noted. 



