CHAPTER XVI 



THE TISSUE ELEMENTS OF SEED PLANTS 



BEFORE we study the microscopic structure of the vege- 

 tative organs of the Seed Plants it is desirable to have 

 some knowledge of the different elements of which 

 the tissues are built up, i.e. of the different kinds of 

 more or less specialised cells ot which the bodies of the 

 higher plants are composed. If we can recognise the 

 elements of the different tissues we meet with in the 

 structure of root, stem or leaf we shall the more readily 

 grasp the way in which these tissues are arranged and 

 interrelated in these organs. 



All the various elements that make up the tissues of 

 a vascular plant are derived from embryonic cells such as 

 are found in the primary meristems at the tips of the 

 branches of the root and shoot (see Chapter VI, p. 102). 

 Most of the body of a herbaceous plant, the " soft " 

 tissues, are composed of living cells with cellulose wall 

 of moderate thickness, and a large central vacuole, 

 so that the cytoplasm forms a layer on the cell wall. 

 The development of such cells from the embryonic 

 cells was described in detail on p. 107. This sort of 

 tissue is called parenchyma, and it forms most of the 

 " ground tissue " of the plant body ; it is also found 

 associated in masses, strands or single cells with the 

 more specialised tissues. The mesophyll of the leaf 

 (pp. 115) is composed of this sort of cell in which the 

 numerous plastids embedded in the cytoplasm have 



