116 



THE BIOLOGY OF A PLANT. 



For this reason many of the cells can only be understood by <a 

 comparison of transverse and longitudinal sections, and these 

 should be studied together until their relations are thoroughly 

 mastered. 



The following table gives brief definitions of the leading 

 vegetal tissues and is good not only for Pteris but for all 

 plants : 



PRINCIPAL ADULT VEGETAL TISSUES. 



These BIX tissues are not only found in the rhizome, but ex- 

 tend throughout the roots and the fronds as well. Moreover, 

 all the tissues not only of the fern but of all higher plants are 

 varieties of them. 



Special Account. It must not be forgotten that the differences 

 between tissues are only the outcome of the differences between 

 their component cells (p. 13). So that the study of the histology 

 of the rhizome, even if preceded (as it may well be) by a dissec- 

 tion, and a naked-eye examination of some of the tissues, event- 

 ually resolves itself into the careful microscopic study of the 

 several kinds of cells composing those tissues. 



The mature parts of the rhizome contain at least nine very 

 different kinds of cells, the characteristics and grouping of 

 which are shown in the following table. In the apical buds, 

 however, this arrangement disappears, and all the cells appear 

 closely similar. 



