270 



THE ANATOMY OF WOODY PLANTS 



inner region which from their topographical relation to the ridges 

 of the stem are known as carinal air spaces. In alternation with 

 these are larger spaces in the cortex situated beneath the furrows 

 of the stem and designated consequently as vallecular lacunae. 



The cortex is largely com- 

 posed in life of green cells 

 and performs the assimila- 

 tive and transpiratory 

 functions inadequately sub- 

 served by the minute leaves. 

 The fibrovascular bundle 

 must now receive further 

 consideration (Fig 193). 

 The tracheary elements are 

 scantily present on the mar- 

 gins of the so-called carinal 

 lacunae. This region is the 

 protoxylem. Outwardly on 

 either flank is seen a row of 

 tracheids which constitute 



the metaxylem. These are 



FIG. 193. Transverse section of bundle of 

 rootstock of Equisetum arvense. 



true scalariibrm or reticulate elements 

 which are laid down after the elonga- 

 tion of the internodes has come to an 

 end. The two masses of metaxylem 

 inclose between them the tissues of 

 the phloem, consisting of larger sieve 

 tubes and smaller parenchymatous 

 cells. In Fig. 194 is shown a longi- 

 tudinal view of the fibrovascular 

 bundles taken a little to one side of 

 the central region. To the left may 

 be seen the carinal cavity containing 

 remains of ringed and spiral protoxylem. To the right appear the 

 reticulate elements of the metaxylem which in the transverse view 

 flank the phloem. 



The organization of the pith and the distribution of the endo- 

 dermal structures in the genus Equisetum are of considerable 



FIG. 194. Longitudinal sec- 

 tion of bundle of rootstock of 

 Equisetum silvaticum. 



