GROWTH OF PLANTS. 



tain intervals and are connected internally with the 

 rows of cells in the cambium. They are structures in 

 which the more delicate forms of cells can best be 

 distinguished, and, at the same time the peculiar mode 

 of growth be discovered. 

 This growth is effected thus : 

 a division takes place in 

 some of the cells, and a 

 transverse septum is formed ; 

 the newly-formed parts con- 

 tinue to grow as indepen- 

 dent elements, and gradu- 

 ally increase in size. Not 

 unfrequently divisions take 

 place also longitudinally, so 

 that the parts become thicker 

 (Fig. 8, c). Every protu- 

 berance is therefore origi- 

 nally a single cell, which, by 

 continual subdivison in a 

 transverse direction (Fig. 8. 

 a, 5), pushes its divisions for- 

 wards, and then, when occa- 

 sion offers, spreads out also 



in a lateral direction. In this way the hairs shoot out, 

 and this is in general the mode of growth, not only in 

 vegetables, but also in the physiological and pathologi- 

 cal formations of the animal body. 



Fig. 8. Longitudinal section of a young February-shoot from the branch of a 

 syringa. A. The cortical layer and cambium ; beneath a layer of very flat cells are 

 seen larger, four-sided, nucleated ones, from which, by successive transverse divi- 

 sion, little hairs (a) shoot out, which grow longer and longer (6), and, by division in 

 a longitudinal direction (c), thicker. B. The vascular layer, with spiral vessels. 

 C. Simple, four-sided, oblong, cortical cells. Growth of Plants. 



