THE ANATOMY OF THE SHOOT 



59 



stored for shorter or longer periods, and because these tissues are 

 comparatively easily crushed or broken and the foods they contain 

 readily released. 



The primary bundles of the stem are typically common bundles. 

 This term was first applied by Hanstein as referring to those bundles 

 that are common to both stem and leaf, in contrast to cauline 

 bundles, which originate in the stem and have no direct connection 

 with the leaves. The common bundle originates at or near the 

 base of the leaf primordium, and one extension of it forms a vein of 



lb 







"m^'^'- 



Fig. il. Transection of a sector of a stem of Raphanus showing the vascular cylinder with 

 the bundles forming a dictyostele. The phloem is subtended by groups of pericyclic fibers 

 and the xylem is surrounded by thick-walled connective tissue. The ray parenchyma has 

 also become thick-walled and there is a limited development of interfascicular cambium. 



the leaf while the other follows an approximately perpendicular 

 course down the stem axis. After traversing one or more inter- 

 nodes, it usually anastomoses with the common bundles of lower 

 leaves. Cauline bundles may be cross-connected with common 

 bundles by branches or by the development of secondary vascular 

 tissue. 



The bundles which comprise the dictyostele are usually collateral, 

 although bicollateral bundles are not uncommon in certain plant 

 families. (Fig. X3.) In the collateral bundle, the xylem and 

 phloem lie on the same radius with the phloem external to the 



