Aug. 2. 1920 Daily Development of Kernels of Hannchen Barley 409 



that length was more dependable than lateral diameter and that lateral 

 diameter was more dependable than dorsoventral diameter in the descrip- 

 tion of types. The same obser^'^ations have been made, presumably, by 

 many others. The growth curves confirm this opinion. The length is 

 quickly attained and should vary little with season. The lateral diameter 

 reaches its maximum more slowly than the length, but much sooner 

 than the dorsoventral diameter, which is dependent upon conditions 

 throughout the growing season for the fulfillment of its maximum pos- 

 sibilities. 



As has been inferred before, the kernels at the base and the tip of the 

 spike are more variable than those near the center. With the increase of 

 the number of kernels on the spike those at the extremes are likely to 

 suffer from competition. On any spike, if nutrition at any time becomes 

 insufficient, the basal and the apical kernels are the first to be affected. 

 Averages which include these kernels show greater fluctuations than 

 those from which they are excluded. This variation was overcome 

 partially by including in the averages no basal kernels which weighed 

 less than half as much as the kernel next above. Since this does not 

 entirely overcome the difficulty the average length, lateral diameter, and 

 dorsoventral diameter of kernels 6, 7, and 8 are plotted in figure 5 as an 

 illustration of the behavior of more typical kernels. It will be seen that 

 the daily fluctuations are much reduced. 



EFFECT OF POSITION OF KERNEL ON GROWTH 



There are two main factors that affect the relative size of kernels. 

 These are age and the position of the kernel on the spike. The relative 

 importance of these factors varies with the stage of growth. The age of 

 the kernel depends on the time of flowering. The florets of a spike are 

 not all fertilized on the same day. The earliest flowers usually are those 

 located about two-thirds the distance from the base of the spike to the 

 tip. The last to fertilize are the extreme basal and apical florets. The 

 largest florets are found one-third the length of the spike from the base. 

 Presumably, the kernels found in these florets receive more nourishment 

 than those at the tip, especially toward the end of the growing period. 

 The length of each kernel on one side of the spike is shown by days in 

 figure 6. The growth is practically completed in these eight days. As 

 will be seen, florets 8, 9, and 10 are the first to fertilize and to begin 

 growth. By the third day these three kernels have reached their greatest 

 relative advancement. After the second day there is a gradual shift in 

 the peak of the curve as the basal kernels approach the others in total 

 length. By the fourth day kernels 8, 9, and 10 are no longer prominent, 

 and on the fifth day the curv^e is extremely regular. By the eighth day 

 the length growth is complete and the longest kernels are the fifth and 

 sixth. The curve of the eighth is thought to be more typical than that 

 of the seventh. 

 183718°— 20 2 



