1904.] 



The Reduction Division in Ferns. 



89 



somes, supported by that of Sutton,* McClung,f and others, affords 

 strong evidence in favour of the theory that the development of certain 

 characters in the zygote corresponds with the presence of certain 

 chromosomes or groups of chromosomes in the nuclei. 



Cannon! has suggested a " cytological basis for the Mendelian laws " 

 founded upon the occurrence of a qualitative reduction division, and, 

 at a time when the general concensus of opinion among botanists 

 was adverse to such a conception, went so far as to predict the 

 discovery of a qualitative reduction in plants. A somewhat similar 

 suggestion, based upon work on Brachystola (Orthoptera), was inde- 

 pendently made by Sutton.^ 



Cannon's hypothesis consisted in the assumption that in fertile 

 hybrids, as well as in pure races, " the chromosomes derived from the 

 father and the mother unite in synapsis and separate in the metaphase 

 of one of the maturation divisions. . . so that the end is attained that 

 the chromatin is distributed in such a way that two of the cells receive 

 pure paternal, and two cells pure maternal chromosomes, and no cells 

 receive chromosomes from both the father and the mother. "|j 



Thus enunciated the hypothesis is applicable only to " monohybrids " 

 (de Vries) ; it is insufficient to explain the phenomena observed in the 

 offspring of Mendelian hybrids whose parent races differ from one 

 another in respect of more than one pair of allelomorphic characters. 



This was recognised by Sutton,U who was thus led to make a more 

 careful study of the whole division process in Brachystola, paying- 

 particular attention to the positions assumed by the chromosomes. 

 He says (p. 233), "the results gave no evidence in favour of the 

 parental purity of the gametic chromatin as a whole. On the contrary, 

 many points were discovered which strongly indicate that the position 

 of the bivalent chromosomes in the equatorial plate of the reducing 

 division is purely a matter of chance, that is, that any chromosome 

 pair may be with maternal or paternal chromatid indifferently towards 

 either pole, irrespective of the positions of the other pairs, and hence 

 that a large number of different combinations of maternal and paternal 

 chromosomes are possible in the mature germ-products of an individual." 



The view that the gametes may contain both chromosomes of 

 paternal and of maternal origin is strongly supported by the recent 

 results obtained by Valentin Hacker in his study of certain Copepoda. 



* " On the Morphology of the Chromosome Group in Brachystola magna" 

 ' Biol. Bull.,' 1904, vol. 4.* 



f " Spermatocyte Divisions of the Locustidae," ' Kansas Univ. Quart.,' 1902, 

 vol. 11, No. 8 (contains other ref ei*ences) . 



£ ' Bull. Torrey Bot. Club,' December, 1902. 



§ « The Chromosomes in Heredity," ' Biol. Bull.,' 1903, vol. 4, No. 5, p. 251. 

 || Cannon, loc. ext., p. 660. 



1" " The Chromosomes in Heredity," ' Biol. Bull.,' 1903, vol. 4, No. 5. 



