Oct. IS. I9I9 Rate of Absorption of Soil Constituents 



59 



Growth periods. — If we refer now to figures i and 2, it appears 

 that growth may be divided into three periods: a preliminary period 

 of eight to nine weeks from planting (five to six weeks from germination) 



«e- 



i^eAj 6 a 10 II 1^ 16 



Fig. I. — Growth reached by barley at different periods of cutting. Experiment of 1916. 



in which the greatest gain in weight of the plant takes place; a second 

 period of about six weeks, when the rate of gain in total weight falls 

 off noticeably and in the 191 6 experiment becomes negligible (it is 

 during this period that the heads are formed and de\'eloped); and a 



"TTcTaT O 5 7 3 II li 1-5 



Fig. 2. — Growth reached by barley at different periods of cutting. Experiment of 191 7. 



third period of about three weeks, in which there is an absolute loss 

 in weight not only in the plants as a whole but in the various parts, as 

 is shown in both experiments. The first period is one of intense vegetative 



