GROWTH UNDER CONSTANT EXTERNAL CONDITIONS. y ]7 



rapidity, after which the growth becomes again slower, and finally ceases when the 

 organ is fully mature. 



If successive equal intervals of time are represented by T^, T,^ .. .T„, and the 

 increments during these intervals by I^, I2 .. . !,„ then it may be stated as a general 

 rule that — 



for T, T, T3 T, T, T, T, 



we shall have I^ < I^, < I3 < I, > I, > Ig > zero. 



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

 as for the entire organs, and for whole stems from their first formation to the time of 

 their full maturity. This course of growth I have termed The Grand Pen'ocP, or 

 Grand Curve of Growth; since it is at once evident that if the values I^, I2 ....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 of length in each period of twenty-four hours* : — 



Mean temperature. 



io-6°C. 



10-5 

 11-4 



12*2 

 13-4 



i3"9 

 14*6 



150 



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

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



^ Kiippen /. 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 soaking of the ground. Compare the curve in pi. i of the Arbeiten des bot. 

 Inst, in Wiirzburg, Heft II. p. 129. 



3 B 



