38 BOTANY. 



single one. This group of cells occupies approximately 

 the same position in the organs of flowering plants as the 

 apical cell does in the mosses and ferns; it is composed of 

 cells which have the power of indefinite division and sub- 

 division. 



59. The apical cell and its actively growing daughter- 

 cells in its immediate vicinity, or, in the case of the flower- 

 ing plants, the apical group of cells with their daughter- 

 cells, constitute the Growing Point or Vegetative Point of 

 the organ. When this active portion is conical in shape it 

 is also called the Vegetative Cone. 



60. The Differentiation of Tissues into Systems. — It rarely 

 happens that the tissues which compose the body of a plant 

 are uniform. In the great majority of cases the cells of the 

 primary meristem become differently modified, so as to give 

 rise to several kinds of tissues. The outer cells of the 

 plant become more or less modified into a boundary tissue, 

 and the degree of modification has relation to its environ- 

 ment. Certain inner cells, or lines of c ells, become modi- 

 fied into stony tissue, or some other supporting tissue 

 (thick-angled or fibrous tissue), and here again there is a 

 manifest relation to the environment of the plant. 



61. Certain other inner cells, or rows of cells, become 

 modified into tubes, affording a ready means for conduction, 

 and appear to have a relation to the physical dissociation 

 of the organs of the higher plants, in which only they 

 occur. Thus, in physiological terms, there may be a 

 boundary tissue, a supporting tissue, and a conducting 

 tissue lying in the mass of less differentiated ground-tissue. 



62. In different groups of plants the elementary tissues 

 described in previous pages are aggregated in different 

 ways, and are variously modified to form these bounding. 



