RATE OF GROWTH 



*73 



different periods of its life. This is expressed in a generalized 

 form in Fig. 8. 



The early seedling stage is shown by the portion ab, and 

 is characterized by a decretion owing to the young leaves being 

 in a low phase of carbon assimilation activity, and providing 

 less material than is consumed in respiratory processes, an 

 observation which confirms the results of Irving and of Briggs. 

 The phase be corresponds to the morphological development 

 of the plant during which the leaf area per unit dry weight 

 increases to a maximum. Finally the phase cd is the latter 

 part of the plant's life and includes the formation of the 



. 



Fig. 8. — The continuous line represents growth rate and the broken line 

 leaf area per unit dry weight. 



flower and the seed. This portion shov/s two secondary 

 maxima at e and / which are respectively coincident with the 

 appearance of the male and female inflorescences and each is 

 preceded by a minimum, g and h, which corresponds to the 

 early stages of flower development at which epoch there is a 

 marked increase in respiration activity. 



The incidence of the maxima is dependent on environ- 

 mental conditions operating not at the time but at a previous 

 stage in the life of the plant. 



The fact that the curve for leaf area per unit dry weight 

 corresponds with the growth rate curve, indicates the close 

 physiological connection between the relative growth rate and 



