234 TWENTY-FIRST REPORT. 



(2) that we are here dealing not with the curve for a single individual, but 

 rather the average of a number of individuals; (3) that cell division when 

 once initiated requires some little time for completion, and we are here dealing 

 also, to more or less extent, with cumulative results, and hence would noi 

 expect to find so many minor variations. 



The relation between cell division and elongation is not so clearly shown 

 when we compare any individual elongation with that of cell division, and 

 in the light of what has just been said we would hardly expect anything else. 

 But when all the curves are considered we find that the average time for the 

 high points, of the one come near the average time of the low points of the 

 other. 



This same rhythmic or wave-like nature of elongation and cell division 

 is found in all the species studied. In some the waves are of longer duration 

 and hence fewer occur in a 24-hour period ; in others they are shorter, giving 

 more. In Zea everta the minor fluctuations are more numerous, but under- 

 lying them are the larger general waves. 



The outstanding conclusion to be drawn from the data at hand is that 

 there are definite waves or rhythms in both elongation and cell division of 

 these plants, even in constant environmental conditions, but there is no uni- 

 formity in the various curves in regard to the "clock" time of their high and 

 low points. 



