X0.3S4] 



HEREDITY AXD ITS II E AX IX G 



475 



find nothing to say for the defense and scientists in this 

 respect resemble the men of the bar. Certainly there are 

 some outlying- facts, but they are comparatively unimpor- 

 tant. If a sei'ies of important facts should at any time 

 be found which do not fit, the chromosome mechanism 

 should be looked into. It is likely that the explanation 

 will be found in an abnormal chromosome behavior as was 

 the ease in the aphis. 



Practical Conclusions and Discussions 

 If now it be accepted as a reasonable premise that the 

 chromosomes are the chief if not the sole bearers of he- 

 reditary determinants of body characters, and that their 

 behavior is a rough indication of the mechanism of he- 

 redity; what cytological facts, if any, can be made useful 

 at present or in the future to plant and animal breeders? 

 If such data exist, thev should be put to service; if it is 

 likely that such facts can be found, investigations should 

 be undertaken. The broad question may be divided into 

 three parts which will be discussed in regular sequence : 



1. What are the relations of chromosomes to somatic 

 characters? 



2. What are the relations of normal chromosome beha- 



3. "What are the relations of peculiar or unusual chro- 

 nioMuiH' behavior to the transmission of characters? 



Relations of Chromosomes to Internal Characters 

 Some very interesting observations have been made on 

 the relations of internal and external characters to chro- 



Farmer and Digby in a comparative study of the cells 

 of a fern of the genus Athi/riuni with similar cells of three 

 of its varieties, found that the measurements were suc- 

 cessively larger in the three varieties than in the species, 

 and that there was a corresponding increase in the number 

 of chromosomes, the gametic numbers for the species and 

 its varieties being estimated at 76-80, 84, 90 and 100, 



