Ii8 Elementary Biology. 



dodermis lies another layer of cells, also derived from the 

 fundamental tissue, but differing from the endodermis in 

 that the cells contain starch-granules in considerable abun- 

 dance. Forming a zone of irregular thickness within this 



FIG. 47. PART OF A TRANSVERSE SECTION OF FIBRO- VASCULAR STRAND 

 OK Pteris aquilina. (Sachs.) 



~~ ^ u ^f- - 



P, starch-bearing parenchyma ; S, spiral vessel surrounded by proser.- 

 chyma ; gg, scalariform vessels ; s p^ sieve tubes ; b, bast ; s^, endo- 

 dermis outside the phloem sheath. 



inner sheath (sometimes known as the phloem- or bast- 

 sheath) lies the phloem, or bast, one of the two essen- 

 tial constituents of the fibro-vascular strand. The phloem 

 consists chiefly of vessels, along with a small amount of 

 starch-bearing parenchyma. The cells are known as bast 

 parenchyma ; they are closely packed, elongated, and 



