THE DUPLICATION OF A LEAF-LOBE FACTOR IN 
THE SHEPHERD’S-PURSE! 
GEORGE HARRISON SHULL 
Princeton University 
In two previous papers (Shull, 1911, 1914) I have demonstrated 
the existence of two independent Mendelian factors in the shepherd’s- 
purse (Bursa bursa-pastoris), each. of which produces the triangular 
form of capsule. In the latter paper I discussed at some length some 
of the criteria and the significance of such ‘‘duplicate’’ factors. I 
gave also a practically complete list of the relevant literature which 
had appeared before 1914, and called attention to certain miscon- 
ceptions which had found expression in a number of the papers cited. 
It is not necessary, therefore, in presenting a new case of dupli- 
cation of factors in this species, to repeat at any length the discussion 
in this earlier paper. It is important however to direct attention to 
the discussions there presented, since several papers along similar 
lines, or on closely related matters, which have appeared more recently, 
do not include a reference to my paper, even when from the terminology 
used it is evident that the authors have had it before them. Several 
writers are now making the desired distinction between “duplicate”’ 
and “‘plural’’ factors, and it is to be hoped that in the future, in the 
interest of precision and accuracy, all those who discuss size-inheritance 
and related phenomena, will abandon the expression ‘“‘multiple”’ 
factors because of its erroneous implications. 
It has been shown (Shull, 1909, 1910, 1911) that the form of leaf 
in shepherd’s-purse is controlled by certain Mendelian genes which 
have been designated Aa and Bb, the presence of A resulting in an 
elongation of the primary lobes of the leaf, while the B gene divides 
the leaf to the midrib, and brings to light certain characteristic second- 
ary lobing. The several possible combinations of these genes give 
the four rosette types: AB = heteris, aB = rhomboidea, Ab = tenuts, 
and ab = simplex. These four forms are illustrated in Figs. 1-4. 
I have now studied the progenies of a considerable number of 
wild Bursas from places as diverse as Chile, Hawaii, Japan, China, 
1 Contribution from the Station for Experimental Evolution, of the Carnegie 
Institution of Washington, and from the Genetical Laboratory of Princeton Uni- 
versity. 
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