138 Pearl aud Surface. 



It is clear from the method of obtainiug- the quintile distributions 

 that the mean quintile position of the whole population of plants at 

 any moment will be 3'0. That is, if we add together the quintile 

 distributions at any measurement of all the plants in a series the mean 

 of this total distribution will tend to be at the center of the tliird or 

 middle quintile. Further it is clear that if there were no influence 

 other than chance affecting the plants starting in a given quintile the 

 mean quintile position would be ver\' nearly 3'0 at every measurement 

 except the first. It has been shown above that there is some other 

 influence determining the height of the plants in these several groups 

 and this effect is clearly shown in the above figures. 



From these figures it is noted that for plants starting in quintile I 

 there is a gradual rise in the mean quintile position with the advance 

 of the season. Likewise the relatively large plants starting in quintile V 

 gradually come to lie nearer the mean of the population. 



It would be possible to get a measure of these tendencies by 

 fitting straight lines to these means for each group of plants. The 

 slope of these lines from the horizontal would indicate the amount of 

 the regression towards the mean. These lines have not been fitted to 

 the data because it was believed that all essential points could be seen 

 without them. Further since there is only a small number of plants in 

 each group there are a number of irregularities which would unduly 

 influence the result, although on the whole these irregularities are 

 perhaps meaningless. 



Plants starting in quintiles II, III and IV show a number of 

 irregularities in the different series. Thus in Fig. 10 it is seen that 

 plants starting in quintile IV fluctuate very closely about the mean of 

 the population for the remainder of the season. TWs is in accord with 

 the result for this group of plants noted above and shown in Fig. 8. 

 In Fig. 10 the plants starting in (juintiie III, instead of remaining near 

 this value for the remainder of the season, give the subsequent means 

 all above 3. Similar irregularities are noted in the other series. 



The most important point brought out by these figures is that 

 there is, on the average, a tendency for the plants small at the 

 beginning of the season to become relatively larger as the season 

 advances. This change tends to take place gradually so that the mean 

 quintile position of the last measurement is in most cases nearer the 

 general mean than any of the others. In all instances the mean quintile 

 positions of these small plants lie well below the general mean. Thus, 



