PTEEiDOPHYTA— FILICiNiE 



131 



are long, narrow tubes with bluntly pointed ends, and have their 

 sieve-plates more or less regularly arranged along their whole 

 length, being thus marked out into very characteristic areas. 

 They have no companion-cells and no callus. 



Except in the monostelic stems the bundles are cauline. 

 They are always closed, cambium not being present. 



Fig. 887. 



Fig. 887. Section of stele of Fern. The upper part is transverse, the 

 lower longitudinal, e. Endodermis. p, jpericycle. s. t. Sieve-tube. 

 X. Xylem. /. Fibres of bast. 



The primary root is in all cases developed, but it usually 

 soon perishes, and its work is taken over by adventitious roots 

 which are produced in great numbers from the stem or the 

 leaf-stalks. Each originates in the endodermis of one of the 

 steles, opposite to a xylem bundle. By the formation of two 

 walls a pyramidal apical cell is cut out of one of the cells of the 

 endodermis, and by successive divisions it gives rise to the 



K 2 



