xiv] SUMMARY 239 



of the hydrocarbon represents the effect produced by sub- 

 stituting a chromosome "bearing" one factor for a chromo- 

 some bearing another. Just as the hydrocarbon radicle is 

 not negligible, since the compounds CH 3 C1 and CH 3 OH 

 differ considerably from C 2 H 5 C1 and C 2 H 5 OH, so the cyto- 

 plasm is not in any sense a negligible factor, but it is never- 

 theless true to say that the substitution of a hydrogen atom 

 by a hydroxyl radicle ( H by OH) turns a hydrocarbon 

 into an alcohol, and in the same way it may be true to say 

 that the replacement of one chromosome by another in cyto- 

 plasm of a generally similar character may be the cause of 

 the production of a definite inherited character. If the words 

 are used in some such sense as this, the statement that in- 

 herited characters are due to factors borne by chromosomes, 

 whether true or false on other grounds, cannot be refuted by 

 the argument that the cytoplasm is not without effect in 

 hereditary transmission. 



Quite shortly, the evidence for the transmission of here- 

 ditary characters by chromosomes may be summarised as 

 follows: (i) the nucleus must be the chief factor in here- 

 ditary transmission, since the spermatozoon consists of 

 little else, and yet in respect of most characters the male 

 and female parents are equivalent. Also experiments with 

 non-nucleated fragments of eggs, and with " partial fertilisa- 

 tion, " indicates that the nucleus plays a predominant part 

 in the production of certain characters. 



(2) A definite relation between abnormal chromosome 

 numbers and hereditary characters is known in Oenothera ; 

 and in the giant tetraploid race of Primula studied by 

 GREGORY, the peculiar type of Mendelian segregation corre- 

 sponds with the behaviour of the chromosomes. 



(3) The whole behaviour of the chromosomes in the ma- 

 turation divisions of the germ-cells provides exactly the 



