GROWTH UNDER CONSTANT EXTERNAL CONDITIONS. 817 



This rule holds good for the separate zones of roots, internodes, and leaves, as well 

 as for the entire organs from their first formation to the time of their full maturity. 

 This course of growth I have termed Tke Grand Period^, or Grand Curve of Growth; 

 since it is at once evident that if the values Ij, \ .... I„ are drawn as ordinates with 

 the intervals of time as abscissae, a curve will be obtained which, starting from the 

 axis of abscissae, reaches a maximum of elevation, and returns again to the axis. 

 The following examples will render this more clear. 



Koppen^ found the following increase of length attained in periods of twenty- 

 four hours with a nearly uniform mean temperature : — 



In an internode of the flowering stem of Fritillaria imperialis I found the fol- 

 lowing increase in length in each period of twenty-four hours * : — 



Mean temperature. 



March 20 2*0 mm. io-6°C. 



21 5*3 io*5 



22 6-1 11*4 



23 68 12-2 



24 9'3 7-5 mm. 13-4 



25 13-4 125 139 



26 12*2 12*5 14*6 



27 8-5 / 11-5 15-0 



28 io'6 14*2 14-3 



29 io'3 126 12*4 



30 

 31 



120 



II'2 



April I 5*8 18-2 107 



2 44 i.*^'.^ 10*2 



^ ' Grand period,' in contrast to the small periodic oscillations of growth which, if represented 

 graphically, would appear as smaller elevations and depressions on the grand curve. 



2 Koppen, /. c. p. 48, I have calculated the daily growth from the lengths given in his tables. 



^ That is, the root together with the hypocotyledonary portion of the stem. 



* A few irregularities in the course of the growth are explained by the temporary acceleration 

 of the growth from the watering of the ground. Compare the curve in pi. i of the Arbeiten des bot. 

 Inst, in WUrzburg, vol. I, Heft II. p. 129. 



3 G 



