GROWTH RATE 



109 



ratio curve is the leaf area in square centimetres per gram of 

 dry weight plotted against time. 



The growth rate of the maize varies much in magnitude at 

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

 form in Fig. 7. 



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 observa- 

 tion which confirms the results of Irving and of Briggs. The 

 phase be corresponds to the morphological development of the 



FIG. 7. The continuous line represents growth rate and the broken line leaf area 

 per unit dry weight. 



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 flower and the seed. 

 This portion shows two secondary maxima at e and f 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 develop- 

 ment at which epoch there is a marked increase in respiration 

 activity. 



The incidence of the maxima is dependent on environmental 

 conditions operating not at the time but at a previous stage in 

 the life of the plant. 



