284 



GROWTH 



periods of rest; Additions to the volume of a plant, like addi- 

 tions to the volume of a cell, are also accompanied by permanent 

 alterations in the form of the body. Unequal accretions along 

 the various axes, and development of new members are the prin- 

 cipal causes to which change of form may be directly ascribed. 



This unequal growth is due to 

 the localization of the generative 

 tissues, or growing points. Ad- 

 ditions to the body may only oc- 

 cur in the vicinity of growing 

 regions, or cambium layers. 



Growth of the body is not al- 

 ways attended by an increase in 

 the gross weight. Thus during 

 the earlier stages of development 

 of a seedling, the combustion of 

 material stored in the endosperm 

 may be so great that the gross 

 and dry weight decrease during 

 the process, and the same is true 

 of the germination of such for- 

 mations as the tuber of the po- 

 tato. Again, in the later stages 

 of the life of the larger plants, the 

 accretions from the formation of 

 new material may not counter- 

 balance that used in the liberation 

 of energy, with no consideration 



FIG. 135. Measurement of growth of 

 the apical portion of a stem of bindweed. 

 A t showing terminal portion of stem with 

 marks of India ink I cm. apart. B, same 

 24 hours later in which the elongation of the 

 various sections may be seen. The maxi- 

 mum rate of growth has been shown by the 

 5th interval from the apex (See Fig. 136). 

 After Bonnier and Leclerc du Sablon. 



