102 



BOTANY 



PAKT I 



xylem portion, and the sieve or phloem portion. While each 

 portion may form independent strands, they are generally united in one 

 VASCULAR bundle (Figs. 117-119). Other terms often used to designate 

 the vascular bundles are eibro-vascular bundles and mestome. The 

 vascular portion is also termed the xylem or hadrome, and the sieve- 

 tube portion the phloem or leptome. The vascular portion contains 

 trachea and tracheids as most essential for the fulfilment of its func- 



Fig. 117. — Transverse section of a vascular bundle from the internode of a stem of Zea Ma is. « , Ring 

 of an annular tracheid ; sp, spiral tracheid ; m and m', vessels with bordered pits ; t; sieve- 

 tubes ; s, companion cells ; cpr, compressed protopliloem ; l t intercellular passage ; vg, 

 .sheath ; /, cell of fundamental tissue. ( x ISO. ) 



tion as a water-conductor, vascular elements (a, sp, m, Figs. 117, 118), or 

 tracheids alone, and, in addition, living, elongated parenchymatous cells 

 that may be designated XYLEM or wood parenchyma. In the phloem 

 portion the most essential elements are the sieve-tubes (r), which serve 

 for the conveyance of albuminous matter. They are always accom- 

 panied by other living cells ; either by the so-called COMPANION 

 CELLS (s), or in addition by elongated parenchymatous cells, or by the 

 parenchyma alone. The companion cells are sister cells of the sieve- 

 tubes, for both have arisen by longitudinal division from the same mother 



