VASCULAR BUNDLE. 217 
and have nothing to do with the conduction of substances, they 
must also be separated from the conducting threads or bundles. 
A typical vascular bundle (Fig. 133) consists accordingly only 
of the vascular portion (Fig. 133, x r sg, xylem" in part) and 
the cribrose or sieve portion (Fig. 133, v, phloém? in part). If 
the terms, xylem and phloém, are so comprehended that the 
bast and libriform cells are not regarded as necessary constitu- 
ents of it, the ‘term sieveportion” is synonymous with that 
of phloém, and “ vascular portion ” with that of xylem.* 
The vaseular portion consists of vessels, tracheids, and 
wood-parenchyma. 
The vessels (¢rachee) are very long tubes, which often traverse 
uninterruptedly the entire plant organ, and the walls of which, 
In consequence of unequal growth in thickness, are variously 
thickened (annular vessels, Fig. 134, 133 r, spiral vessels, Fig. 
134, 133 s, trabecular and scalariform vessels, Fig. 135 fv, 133 
g, 142, pitted vessels). They are formed by the disappearance 
of the transverse walls in a row of cells (fusion of cells), In 
coniferous wood, the vessels, as a rule, are wanting (Lignum 
Juniper). 
1 Evdov wood. 
* Protor bark of a tree. 
°For the sake of clearness these terms may be arranged in a table : 
Bast-cells ) 
(mechanical 
elements) 
if = ( Phloém )} % - 
Zo Sieve-tubes and 3 { (Bast) S 
Es Sieve portion Latticed cells fi 3 
a a¢ (Leptom) — a = | 3 
i $; Ls 
BS ma ( + 
= 5 =| Vascular portion | Vessels and | J 
32 (Hadrom), Tracheids | 2 
che L Wood parenchyma a Es 
~ (Wood) J 2 
Libriform 
(mechanical 
elements) 
new old 
division 
