96 COMPENDIUM OF GENERAL BOTANY. 



1. The central arrangement of the conducting elements and 

 the mechanical elements in the root; their more peripheral ar- 

 rangement in the stem. 



2. The centripetal development of primordial vessels in the 

 root ; their centrifugal development in the stem. 



3. The tangential arrangement of the two conducting bundle- 

 portions, that is, the leptome and the hadrome (sieve-portion and 

 vessel-portion), in the root ; their radial arrangement in the stem. 



FIG. 58. 



A, Diagramatic ; B, anatomical representation of the segment x. (After Haberlandt.) 



Ad 2. This anatomical characteristic is perhaps closely related 

 to the first, in that its purpose seems to be to utilize the cen- 

 tral space as much as possible. This arrangement is also ad- 

 vantageous in that it brings the vessels nearer the root-hairs which 

 absorb the moisture from the soil. The vessels first formed (pri- 



