CHAPTER V 



GROWTH AND CELL DIVISION 



The growth of the higher plants is very different from that of 

 the higher animals. In animals growth ceases after a relatively 

 short period in the life of the organism ; plants, on the contrary, 

 continue to grow throughout their whole 

 life, which, as in the case of long-lived 

 trees, may extend over hundreds of years. 

 In the early stages of the growth of a 

 higher plant from the egg cell all parts 

 of the embryo grow until the seedling 

 is thoroughly established for self-support. 

 In annual and biennial plants growth 

 may continue to be general over a large 

 part of the plant body, although it usually 

 becomes localized as maturity approaches. 

 In perennials, however, including our 

 common trees and shrubs, growth and its 

 accompanying cell division is largely lim- 

 ited to the tips of the roots and shoots 

 and to the cambiums, or growing cell 

 layers, which produce annually new lay- 

 ers of wood and bark. Buds are familiar 

 examples of this localization of growth 



Lateral branch^.. 



A 



FIG. 30. Growing areas 

 of a buckwheat plant. 

 The growing parts are 

 stippled; the permanent 

 portions are white 



at the branch tips, and we shall find a similar provision at the 

 tips of roots. Fig. 30 illustrates diagrammatically the growing 

 zones of an ordinary herbaceous plant in which growth has 

 become localized. 



Since growth is one of the most important phenomena in the 

 life of plants, we can profitably devote a considerable space to an 

 account of a concrete case of cell and organ growth, which will 

 furnish a foundation for understanding all growth more clearly. 



60 



