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the frequent recurrence of these variant sectors commanded attention, trans- 

 fers were made from several of them to freshly poured agar-plates, and a 

 transfer from the normal portion of the colony was added to each of these 

 plates at a distance of about 2 cm. from the other transfer. The variant 

 transfer was then marked on the bottom of the doubly occupied plate as 

 M (indicating mutant), and the normal transfer as O (indicating original). 

 In all the early transfers the M transfer resulted in a colony (Ml) of decid- 

 edly slower growth and more profuse conidial production than that pro- 

 duced by the O transfer. The two colonies also differed markedly in general 

 appearance owing to minute single differences which were often difficult to 

 analyze, but which in the aggregate constituted distinctions which were so 

 well-marked and obvious that at first sight one would say that the two 

 colonies were those of two distinct fungi (PI. XXIII, lower fig. ; PI. XXVII). 

 When these colonies grew to fill, or nearly to fill, the plate, transfers from 

 them were made to new agar plates, and later, transfers from these second 

 plates, and so on, the series of transfers being a long one. It was found 

 that the differences appearing in the Ml and Ol colonies were usually 

 maintained on succeeding plates. These findings led to the tentative 

 assumption that forms in the variant sectors were mutants or saltants of 

 a more or less permanent nature, and a more serious study of this phe- 

 nomenon was undertaken. 



In their origin the variants or Saltants always appear as sectors which 

 differ from the portion of the parent colony adjacent to them (see PI. XXII 

 XXV) . To the naked eye the most common deviations from the orig- 

 inal type are in density, color, and rate of growth. Closer observation, with 

 the microscope, frequently shows variation in the grouping, size, and shape 

 of the conidia, and in the branching of the mycelium. Quite often many 

 small sectors of divergent character appear at the edge of a large colony, 

 especially on a plate that is beginning to dry. Many of these divergencies 

 are merely modifications due to local environmental changes, and whether 

 they are more can be determined only by close study of their behavior in 

 subsequent transfer or transfers. Closer consideration of the characters 

 involved in these saltations is best deferred to the following topic. 



In following this discussion it must be borne in mind that M refers to 

 the variant sector on the plate on which it originated; Ml, to the colony re- 

 sulting from the first transfer from M; M-2, to that resulting from the first 

 transfer from Ml, and so on; and that O refers to the original colony in 

 which the M arose. It is my custom to give the saltant a serial number 

 (writing this on the plate in which it was found), and, usually, to transfer 



