n] Meristic Cases 



47 



As yet only one example of a character which can at 

 all readily be interpreted as meristic in nature has been 

 shown to have a Mendelian inheritance. This is the case 

 of the reduction in number of the human phalanges in 

 brachydactyly. We speak of a character as " meristic " 

 when it manifests itself in respect of the number of parts 

 into which the body or one of its organs is divided. Meristic 

 characters are in several ways distinguishable from other 

 features of bodily organisation. The physiological occur- 

 rences which result in meristic variations are in all likelihood 

 distinct from those which produce substantive changes, and 

 exceptional interest would attach to any investigation of 

 the genetic properties of such variations. Polydactylism is 

 of course a meristic feature, but it may involve something 

 more than a divisional change, pure and simple, since 

 change in the number of digits is usually accompanied by 

 change in the distribution of differentiation. A case in 

 which the disturbance of differentiation is not so evident is 

 provided by the cross between Oxalis tetraphylla, much 

 cultivated in Germany as Glilcksklee, and one of the forms 

 with three leaflets. This cross was partially investigated 

 by Hildebrand*, who used O. latifolia. He found that 

 the 3-fold character was an imperfect dominant, the leaves 

 being 3-fold with the exception of occasional 4-fold leaves 

 which appeared for the most part at the flowering period. 

 The hybrids were fully fertile, but their progeny has not 

 been studied. Satisfactory meristic cases from which all 

 confusing elements are eliminated must be rare, but it is 

 greatly to be hoped that they will now be searched for. It 

 is most desirable that cases of difference in the ground- 

 plan numbers of some radial type will be found amenable 

 to experimental tests. Here the problem may be seen in 

 a somewhat simplified form on account of the elimination 

 of serial differentiation f. 



* Hildebrand,/^/^ Ztsch. f. Naturw. 1889, xxm. N. F. xvi. p. 56. 



t Since this paragraph was set up Price and Drinkard's (221) evidence 

 has been published showing the dominance of two chambers in the fruit of 

 the tomato over the many-chambered condition. More evidence as to 

 such cases would be welcome. 



Drinkwater's recent discovery as to the bones of the brachydactylous 

 fingers, showing that the middle phalanx is actually formed as a distinct 

 bone which afterwards unites with the distal phalanx, raises considerable 

 doubt whether the variation in that case is meristic after all. 



