6 



THE AMEBIC AN NATURALIST [Vol. LV 



fowl (a dominant) and the leaf of the monophyllous 

 strawberry with a single leaflet (a recessive) which have 

 a factorial inheritance, but the resulting terms, especially 

 the heterozygotes, are indefinite. In the polydactylous 

 fowl, for example, the heterozygote has a great variety 

 of shapes. The hind toe is most often represented by 

 two sub-equal digits, but the duplicity may be so slight 

 as to appear externally only as a division of the nail. It 

 may also assume another very different form, in which 

 there is only a single many-jointed digit representing 

 the usual pair. In the monophyllous strawberry the 

 homozygous recessive, whether before or after imme- 

 diate extraction from the heterozygote, shows fluctua- 

 tions to a 2- or 3-leaved condition.^ Such fluctuations are 

 common among forms distinguished by meristic pecul- 

 iarities. There are not the uniformity and simplicity 

 which are such striking features of variations in color 

 and many other substantive characteristics. The evi- 

 dence as to meristic differences is, how^ever, still scanty, 

 and it is too soon to decide what importance should be 

 attached to this preliminary impression. 



With more confidence we recognize that merely quanti- 

 tative differences seldom, if ever, have a perfectly simple 

 inlieritance. There are two obvious interpretations: (1) 

 tliat the factors do not usually segregate clean; (2) that 

 the tiiifiiIxT of factors involved is so large that their 

 '■tlVct-^ nic masked. Adequate discussion of these two 

 P<->MlMliti(.s could only be given at considerable length. 

 On the whole, I incline to the former alternative, but the 

 material for a decision scarcely exists as yet. Certain 

 example, should be noticed in which, though the most ob- 

 Mon. diflVrentiatinu- feature (,uantitati ve, the under- 

 i^';'- J'l'^^i"l"^'i''>l dl^tiH.-tiuM uuu-v prnhably to be 

 '" 'i"<'l'tJtti'' «' lactm. liriuht in certain 

 l'i;iiit> i> ;i --(Mxl iHii.-trntion. It i> ostensibly a (luantita- 



>ut in various cases, c.f/., peas and sweet peas, 

 are aUo a diu ker green. The dwarf of Cam- 



