SHULL: DUPLICATION OF A LEAF-LOBE FACTOR 429 



Australia, Tasmania, India, Ceylon, South Africa, the Sahara, and 

 from widely distributed points in Europe and North America, and find 

 that the forms everywhere fall into one or more of these four rosette 

 types. This does not mean, however, that with respect to leaf- form 

 there are only four biotypes of this species in existence, for nearly 

 every lot of material from a new locality presents minor details of 

 lobing which lead to their easy recognition as new and distinct biotypes. 



In all of the earlier crosses between types respectively dominant 

 and recessive for either of the above-mentioned character-pairs, there 

 appeared in the F2 close approximations to the monohybrid ratio, 

 3:1, or undoubted modifications of that ratio, — the modifications 

 being due, in most cases at least, to the facts (a) that the A factor has 

 been in some combinations not completely dominant, and (b) that 

 both A and B require for their manifestation a certain minimum oppor- 

 tunity in the way of favorable environment, including cultural treat- 

 ment. 



These results having been well established while the situation in 

 regard to the capsules called for further extensive investigation, a 

 number of my cultures which concurrently involved the rosette char- 

 acters and the capsule characters, have been grown under conditions 

 not ideal for the development of the leaf lobes, though adequate for 

 the determination of capsule form. For this reason my records with 

 respect to the leaf types in certain families are of such incompleteness 

 as to make the recorded ratios of no particular value. In nearly all 

 cases, however, a small portion of each pedigree has been given suf- 

 ficiently good treatment that the composition of the several families 

 with respect to the rosettes could be inferred with small probability 

 of error. 



The discovery to be detailed below, that in certain races there are 

 two independent Mendelian factors which affect the leaf-form in 

 identical ways, each dividing the leaf to the midrib and bringing out 

 the secondary lobing which is seen unmodified in rhomboidea and modi- 

 fied by the action of the A factor in the case of heteris, has revived my 

 interest in the inheritance of the rosette characters and investigations 

 are now in progress which I hope will give in time a full insight into 

 the composition of the rosettes with respect to the major factors affect- 

 ing the leaf lobes. 



The duplication of the gene which produces the triangular capsule 

 has been found almost universally distributed geographically, as will 

 be shown in detail in a later report, but the duplication of the leaf- 

 lobe factor, B, appears to be relatively much less frequent. 



Before presenting the evidence of dimery in respect to the B 

 lobes of the leaves, it will be advantageous to have before us the 



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