Growth and variation in maize. 1 ] 3 



After June 19 there is a period of rapid decrease ia the relative 

 variability. This decrease continues until the plants begin to tassel or 

 about the first of July. This decrease in the coefficient of variation is 

 probably an expression of the general growth law of diminishing varia- 

 bility refen-ed to above. It will be noted from Fig. 2 that during this 

 period the absolute variability remains nearly constant indicating that 

 the plants are all growing at about the same rate. This would indicate 

 that plants retarded during the first growth period do not make up for 

 their loss during this second period. 



With tlie exception of series B the plants began to tassel about 

 July 3, and there is no noticeable increase in the average rate of growth 

 (Fig. 1) before this time. However, the effect on the variability is 

 noticeable earlier than this. Thus series A, which was the first to 

 tassel, showed only three tassels on July 3, yet at this date it exhibits 

 a marked increase in its variability, both absolute and relative, over 

 that of the preceding measurement (June 29). During the period in 

 which the tassels make their appearance, July 3 to 10, there is a very 

 rapid increase in variability. This means that certain plants, having a 

 tendency to tassel earlier than the others, grow in height much faster 

 than their neighbors during this period. After the tassels have appeared 

 on all the plants, the varial)ility, both absolute and relative, begins to 

 decrease. TMs decrease is quite rapid and continues until all the plants 

 have attained their final height. This decrease in absolute variability 

 indicates that here those plants which tasseled first and grew very 

 rapidly grow much slower as they approach maturity, while the late 

 tasseling plants grow very rapidly and thus tend to decrease the dis- 

 persion about the mean. In the later measurements (July 20 and 24) 

 some of the plants have already attained their final height, while others 

 continue to grow. 



It is of interest to note that in the tassel measurements (series I), 

 E and F) the variability, both absolute and relative, reached a greater 

 height than in the case of the leaf, measurements (series A, B and C). 

 Further the decrease in variability begins much earlier in the leaf 

 measurement series than in the tassel series. These facts are in 

 agreement with those previously discussed, and shown in Fig. 1, namely 

 that the plant reaches its final height as shown by leaf measurements 

 much earlier than in the case of the tassel height. Thus the upper 

 node, of which the tassel is a part, continues to grow after the lower 

 nodes have ceased. The changes in variability show that the growth 



Induktive Abstammungs- und Vererbungslehre. XIV. g 



