HARRIS: TETRACOTYLEDONOUS RACE OF PHASEOLUS VULGARIS 237 



cidedly asymmetrical, the mode lying above the mean. There 

 seems no obvious advantage in fitting theoretical curves to these 

 observed frequency distributions, at least until wider series of data 

 grown under experimentally controlled conditions are available. 

 The variation constants for number of cotyledons are as follows. 



Mean 



Standard deviation 



Coefficient of 

 variation 



Less mature series 



More mature series 



Difference 



More and less mature combined 



3.686 ± .023 



3.755 ±.015 



.069 ± .028 



3.730 ± .013 



0.716 ± .017 

 0.616 ± .011 

 o.ioo ± .020 



.654 ± .090 



19.43 ± 46 



16.40 ± .29 



3-03 ± -55 



17.54 ± -25 



Thus there is an average of about three and seven tenths coty- 

 ledons per plant, with an absolute variation as measured by the 

 standard deviation of about seven tenths of a cotyledon, or seven- 

 teen to eighteen per cent. 



The question of the relationship between the character of the 

 axis and the number of cotyledons can not be discussed in detail 

 here. The accompanying table shows the average number of 

 cotyledons for each type of axis. 



^ 



Mean number of cotyledons 



Class of axis 



Less mature series 



More mature series 



Both series 



It is clear that there is no intimate dependence of cotyledon 

 number upon the structure of the stem. If the comparison be 

 reduced to that between plants with axes normal or only slightly 

 broadened^ and those with axes much broadened or divided, the 

 results are: 



^ The combination of these two classes seems to be necessary because of the difficulty 

 of distinguishing sharply between them. 



