68 Study of Right- and Left-Handedness 



These results are very striking, and as Church remarks, " The 

 element of chance appears quite out of the question" in the case of 

 P. laricio. 



It may be suggested that perhaps differences in conditions (sunlight, 

 prevailing winds, etc.) between opposite sides of the tree may have 

 caused an excess of cones to arise towards one side : and that, since the 

 genetic spiral of a lateral branch depends on its mode of insertion, this 

 might be the cause of the excess of one kind of spiral among the cones. 

 At present, however, it is impossible to decide whether this accounts 

 for the phenomena, or whether there is a definite tendency in the apical 

 meristem to produce a genetic spiral of one direction rather than the 

 other. 



Conclusions. 



The present paper deals with the dimorphism found in certain 

 Gramineae in respect of the mode of folding of the first leaf of the 

 young plant. It is in part a continuation of a previous paper (cited 

 above) to which reference should be made for an explanation of the 

 conventions used in describing the phenomena, and for a summary of 

 the literature of the genetics of right- and left-handedness in general/, 



^ Further references to works on the genetics of right- and left-handedness may be 

 inserted here. 



H. E. Jordan ("The Inheritance of Left-Handedness," American Breeders^ Magazine, 

 Vol. II. pp. 19, 113 : 1911) gives a number of human pedigrees which show that functional 

 left-handedness is hereditary, in certain cases apparently in conformity with a simple 

 Mendelian scheme. The most remarkable human pedigree on record is perhaps that 

 given by Aim6 P6r6 (Les courbures laterales normales du rachis humain, Toulouse, 1900, 

 p. 71 : quoted by D. J. Cunningham, "Eight-Handedness and Left-Brainedness," Journ. 

 Anthropol. Inst, xxxii. p. 273, 1902). In this family no fewer than twenty-six left-handed 

 individuals are recorded : the marriage of a LH ? x RH i gave eight sons and six daughters, 

 all left-handed, — a fact in strong contrast to Jordan's hypothesis of the dominance of 

 right-handedness, and suggesting the reverse assumption. A number of other instances 

 of inheritance of left-handedness in man are given by F. Lueddeckens (Rechts- und Links- 

 hdndigkeit, Leipzic, 1900). A general summary, with a full bibliography, of our present 

 knowledge of human asymmetry is given by K. von Bardeleben ("Ueber bilaterale Asym- 

 metrie beim Menschen und bei hoheren Tieren, " Anat. Anz. Ergdnzungsh. z. Bd. xxxiv. 

 p. 2, 1909). 



H. de Vries, The Mutation Theory (Engl, trans.), ii. p. 561, London, 1911, finds that 

 the peculiar torsion of the stem in certain races of Dipsacus sylvestris is partly hereditary, 

 but that the direction of the twist is not transmitted. About equal numbers of RH&nd. LH 

 individuals are produced normally : and in an experiment in which only RH plants were 

 allowed to flower in two successive years the offspring comprised 245 RH and 239 LH 

 plants. 



