PERIODICITY OF GROWTH 295 



uniform at all stages of development, or at all parts of the day. 

 An analysis of the curves shows that the rate is slow at first, in- 

 creasing rapidly to a maximum and then decreasing to a minimum, 

 or entire cessation upon the full stature of the organ being reached, 

 the entire action constituting the grand period of growth of the 



Fig. 142. Registration, and curves of growth of leaf of Hyacinthus Belgicus, 

 showing daily variations. The upper figure shows actual tracings of pen of precision 

 auxanometer (Fig. 139). The line E-Fis the record of growth during three nights 

 and two intervening days ( 63 hours); US, for 88 hours. Lower figure. G-H, curve 

 of growth showing daily variations. The maximum occurs between midnight and 4. 

 A. M., and the minimum about noon, at which time it is nearly zero. A comparison 

 with the thermograph curve, T-M, shows that the minimum growth takes place at the 

 highest temperature, and is indicative that this temperature is above the optimum for 

 the species. XII denotes midnight ; 12, noon. 



organ. If the growth of a stem is followed by actual calibration 

 of the elongating internodes, it will be found that the approaching 

 termination of the period is marked by many irregularities. 

 Among these, it may be mentioned, that variously distributed 

 regions of narrow limits continue a slight increase after the main 

 regions have ceased. 



