OHAPTEE III. 

 THE GROUPS OF TISSUES, OR TISSUE-SYSTEMS. 



55. Primary Meristem. — The ends of young stems con- 

 sist of rudimentary tissue {meristein), from which all the 

 tissues formed in the plant are derived. As these stem- 

 ends grow there is a continuous formation of additional 

 meristem in the newer portions, while in the older por- 

 tions the rudimentary tissue is changing into permanent 

 tissues. There is thus always an advancing terminal mass 

 of meristem, from which all the tissues of the stem are 

 developed. This original rudimentary tissue is appropri- 

 ately named the Primary Meristem. 



56. In most plants below the flowering plants the pri- 

 mary meristem is produced by the continually repeated 

 division of a single mother-cell situated at the apex of the 

 growing organ. In the simplest forms this apical cell is 

 the terminal one of a row of cells, as in many seaweeds and 

 fungi. The apical cell, in such cases, keeps on growing in 

 length, and at the same time horizontal partitions are 

 forming in its basal portion. In this way long lines of 

 cells may originate. 



57. In the more complicated cases the segments cut off 

 from the apical cell grow and subdivide in different planes, 

 so as to give rise to masses of cells. The partitions which 

 successively divide the apical cell are sometimes perpendic- 



36 



