442 BROOKLYN BOTANIC GARDEN MEMOIRS 



at Bremen and Berlin, Germany, and perhaps at Peking, China, while 

 monomeric B lobes (Table i) have been demonstrated in strains from 

 all these places except Tucson, Arizona. Besides these places in 

 which the two types have been found associated together, the mono- 

 meric condition has been found at Chicago, Illinois, at New Carlisle, 

 Ohio, at Landau, Germany, and probably at Vicenza, Italy, in which 

 places duplicated factors for this character have not yet been dis- 

 covered. Excepting only Landau, Germany, these localities in which 

 duplication of the B factor has not yet been found, have been repre- 

 sented in my cultures by only one wild 5-lobed plant from each 

 locality. It may be merely a matter of chance that the first plant 

 from each of these localities had but one of the B factors. It should 

 also be noted that from the only region in which monomeric B lobes 

 have not been found, namely at Tucson, Arizona, only two wild 

 plants have yet been tested, a number quite too small to give any 

 confidence in the suggested inference that no biotypes with monomeric 

 B lobes occur at that place. It is obviously necessary to make the 

 study of geographical distribution of these B factors much more 

 extensive before safe conclusions may be drawn as to the primitive 

 or derivative condition of the B lobe with respect to duplication. 

 This is a work in which many students might lend assistance by 

 crossing together the several wild biotypes from their own localities. 



Summary 



The leaf lobes of shepherd's-purse are controlled by Mendelian 

 factors A, producing elongated sharp lobes, and B which divides the 

 leaf to the midrib and brings to light certain characteristic secondary 

 lobing. The action of these factors is easily suppressed or obscured 

 by unfavorable environmental conditions, and the inheritance ratios 

 are usually more or less defective on this account. In previous papers 

 both of these characters have been reported to be monomeric, i. e., 

 each was found to be controlled by a single factor. 



It is shown in the present paper that two factors, B and B', exist 

 in certain strains and that these two factors produce the same char- 

 acteristic lobing of the leaves, but are inherited independently of each 

 other and of the factor A. 



The biotypes having the B factor duplicated appear to be less 

 widely distributed than those which are monomeric with respect to 

 the B lobes. More extensive data are needed on this point, but if 

 the present indications are confirmed, the relatively less frequency of 

 the dimeric condition is taken to mean that the duplication of this 

 factor has taken place at a relatively recent date. 



