580 WHITE— STUDIES OF INHERITANCE IN PISUM. 



" Rogues." 



The term " rogue " is applied by seedsmen to any variation or 

 off-type plants in a field of pure-bred plants of a variety. For ex- 

 ample, tall peas in a plot sown to dwarf peas, colored-flowered indi- 

 viduals in a white-flowered variety, yellow seeds in a green-seeded 

 variety, late bloomers in an early-flowering variety are all desig- 

 nated as rogues and carefully eliminated. In many cases, these 

 rogues are due to careless handling of the seed ; in others, to the 

 presence of heterozygotes which svibsequently produce recessives — 

 the heterozygotes having arisen through rare insect crossing or 

 through never having been selected out when the variety was first 

 placed on the market, e. g., Nonpareil and others with yellow and 

 green cotyledons. Again, these " rogues " may come about through 

 " recurring mutation " phenomena or through regular mutation. In 

 Tschermak's studies on flower color and maple seed coat, certain 

 factors appeared in exceptional cases to be present but inactive. 

 Thus among pink-flowered peas, plants with purple red flowers 

 might occasionally appear. Still another way in which " rogues " 

 could easily occur has its basis in a change in environment and in 

 the fact that all factors or factor combinations do not react alike 

 to such changes, so that while under one environment a variety 

 might breed true, under another, variations would appear, due to 

 unsuspected factorial differences. 



Most of these rogues can be eliminated permanently by removing 

 the cause, but those that result from recurring mutations can, so 

 far as we now know, only be reduced to a minimum and kept there 

 only by constant watchfulness. 



Coupling (Linkage) and Crossing-Over. 



Varieties of peas so far investigated have seven pairs of chromo- 

 somes (Cannon, ii). If the genetic factors of animals and plants 

 are located in the chromosomes as believed by Morgan (62) and 

 others (61, 62.5, 26.5, ^2))^ ^^^ the factors of a single variety 

 of peas should be inherited as though linked or coupled together in 

 seven groups, each group representing the factor composition of one 

 of the seven pairs of chromosomes. This grouping in peas can be 

 determined with the least trouble by crossing a variety having seven 



