730 



RESISTANCE OF FOLIAGE-STEMS TO STRAIN, PRESSURE, AND BENDING. 



laterally with one another, and form what may be regarded as a link connecting 

 this with the following group. 



The second group comprises all stems in which the flanges of numerous simple 

 girders are fused laterally so as to form a cylindrical tube. This tube lies as near 

 to the periphery as possible, and consists of hard bast developed from the bast 

 portions of the originally distinct vascular bundles. In consequence of this the 

 vascular bundle is always in connection with the hard bast tube. The various 

 methods of connection, and the presence or absence of accessories to this bast tube 



Fig. 179. — Transverse sections of erect foliage-stems with simple girders fused into cylindrical tubes. 



I Crow Garlic (Allium vineale). 2 Carnation {Dianthus Caryophyllus). s Polygonatum verticillatum. * Purple Molinia {Molinia 

 carulea. * Woodruff (Asperula odorata). ^ Sumbul {Euryangium Sutnbul). In these diagrams the mechanical tissue is 

 represented grey, and the vascular bundles blacl: with white spots. 



in its resistance to flexion, give rise in this group to a great multiplicity of structure. 

 Some of the most interesting forms are represented in fig. 179. In fig. 179'^ the 

 cross section of the stem of a Carnation {Dianthus Caryophyllus), the vascular 

 bundles are situated on the inner side of the bast ring; in fig. 179 \ a transverse 

 section of the stem of a species of garlic {Allium vineale), the bundles are partially 

 embedded in the outer part of the bast ring, and in 179^, a transverse section of the 

 stem of a species of Solomon's Seal {Polygonatum verticillatum.), the bundles are 

 wholly embedded in the ring of bast. The first case is by far the most common, and 

 may be regarded as characteristic of most dicotyledonous herbs and undershrubs; the 

 second case obtains in many bulbous plants; whilst the third, the rarest of all, is 

 only found in a few monocotyledons. The accessory parts occur either as band-like 



