116 Pearl and Surface. 



of the tassel and the resultiag fertilization of the car, about August 1. 

 During this time there is a very rapid increase in the height of the 

 plant. Also during the first part of this cycle there is a rapid increase 

 in both absolute and relative variabUity. Tliis is followed in the second 

 portion of the period by a decrease in vaiiability, so far as the height 

 of the plants is concerned. 



This period is followed by the fourth or ear growth cycle. Tliis 

 extends from the time of fertilization until matuiity. During this period 

 there is no increase in the height of the plant. Since we have no 

 data regarding the growth of the ear itself this cycle cannot be dis- 

 cussed in detail. 



While there is much in the Literature to indicate that growth 

 often takes place in cycles, it appears from the present data that these 

 cycles are particularly well marked in the corn plant. 



Summary of Part I. 



Measurements were made at twice-a-week intervals of the height 

 of three series of maize plants. The heights were measured to the tip 

 of the tallest leaf. In addition to these, separate sets of measurements 

 were also made of the tassel height as soon as the tassels appeared. 



The growth curves obtained liy plotting the mean height at each 

 measurement are relatively smooth. (Fig. 1.). 



After July 3, the time of tasseling, the plauts grow in height much 

 faster than before. Growth in height ceases entirely as soon as the 

 tassel blooms. 



The al)solute variability (Fig. 2) shows a marked increase up to 

 about June 19. From this until the time of tasseling it remains nearly 

 constant but shows a very gi-eat increase at the time of tasseling. 

 After all the plants have tasseled the absolute variability decreases 

 somewhat. 



The relative variability considered for the whole season (Fig. 3) 

 shows a marked progressive diminution. It thus follows the general 

 growth law of diminishing variability. Considered in detail, however, 

 the relative variability first shows an increase. After June 19 there is 

 a rapid decrease until the time of tasseling. During the period of 

 tasseling there is a very rapid increase in the relative variability. This 

 is followed by an equally rapid decrease. A stable condition is finally 

 reached which is some ten percent lower than the variability at the 

 beginning of the season. 



