288 METAMORPHOSIS 



Indian ink i mm. apart, and found that in the following days this zone increased 

 in length in accordance with the following numbers : — 



Days ....I 2 3 4 5 6 78 



Increase in mm. 18 37 17.5 165 170 145 7.0 o 



The rate of growth at first is slow and then rapid ; the maximum rate is 

 maintained for a certain time, later on it decreases and finally ceases altogether. 

 This phenomenon, which has been observed in all cases where growth has been 

 measured, has been termed by Sachs (1872) the ' grand period of growth '. 



We will now mark out with Indian ink on a root not one transverse zone 

 only, but several, beginning at the growing point, and passing backwards, each 

 being i mm. apart. If we calculate the increase in relative length of these 

 zones on the following day we shall find that the increase is different in each 

 zone, but that the differences are undoubtedly subject to certain laws. A few 

 examples will make this clear. In the following table the several zones marked 

 off from the growing points are indicated by the numerals I, II, III, &c., and 

 the growth-increase during 22-24 hours is indicated in mm. (means of several 

 measurements) : — 



Viciafaba (Sachs, 1873) 

 Viciafaba (Popovici, 1900") 

 Phaseolus (Popovici, 1900) 

 Peas (Sachs, 1873) 



It will be seen from these different examples that only a few of the zones 

 marked out on the root are growing in length, and that the grand period begins 

 at I and ends at XII. In order to obtain a better conception of the periodic 

 changes in rate of growth in the individual zones we will attempt to give 

 a graphic representation of the example (Vicia jaha) first cited. We will repre- 

 sent the time in hours by abscissae, and the lengths of the zones at the beginning 

 of the experiment and after twenty-two hours by ordinates, and endeavour to 

 draw curves indicating roughly the successive increments of growth (Fig. 85), 

 assuming that growth as a whole is uniform, and that the length of the growing 

 zone remains 10 mm. in length. This mode of representation shows very clearly 

 that the upper zones, after a very brief interval, have completed their growth, 

 while the lower ones, usually after several hours, begin to elongate. We see that 

 a certain zone, the third in the figure, has attained the greatest length, and we 

 also see that the position of maximum growth must shift as time goes on, 

 always approaching the apex. To make this clearer still we will express Fig. 85 

 by a series of measurements as in the following table. The zones, each i mm. 

 long, have increased by lengths corresponding to the successive numbers 

 indicated (in mm.) : — 



Hours: o 3 6 9 12 15 18 21 



X. 10 1.2 growth completed 



IX. 10 1.5 „ „ 



VIII. i.o 1.8 „ „ 



VII. i-o 1-8 2.0 growth completed 



VI. 1.0 1.6 2-8 „ „ 



V, 10 1-2 2.8 4-2 4.6 growth completed 



IV. i-o LI 1.4 3.3 j-.o 64 growth completed 



III. 10 10 1.2 1-4 2-2 4.4 6-8 8-6 



II. 10 I.Q LO I'D 1-2 1.2 1.8 30 



I. 1.0 1.0 I-o 1.0 I-O 1.0 1.2 1.6 



We see from this that the maximum growth is reacned after three hours in 

 the zones VIII and VII, after six hours in VI and V, and steadily advances 

 thereafter until, after eighteen to twenty-one hours, it occurs in zone III. If 

 we were to allow more time to elapse between each two measurements we should 



