328 



GENERAL BOTANY 



cylinder in a two-year-old stem of a spruce are diagrammati- 

 cally shown in Fig. 194. In the lower part of the figure the 

 cortex and one annual ring of wood are represented as having 

 been removed so as to expose the outer surface of the wood of 

 the first year. On this exposed surface the leaf gaps appear as 

 in the vascular cylinder of the maidenhair fern (Fig. 170). In 

 the upper portion of Fig. 194 the pith is removed and the long 

 leaf gaps are visible on the inside of the wood cylinder. In the 



Tracheids 



. 



Wood ray a b '"* parenchyma; 



FIG. 193. Structure of the wood of the spruce (Picea) 



a, transverse section ; 6, long section. Copied from Jeffrey's " Anatomy of 

 Woody Plants " 



partial cross-section view at the junction of the upper and lower 

 portions of the figure the pith is seen to continue into the leaf 

 gaps and in a living stem would be continuous with the cortex 

 through the gap during the first year's growth. This struc- 

 tural feature is also shown in the first annual ring of wood 

 as it appears in actual sections of one- and two-year-old stems 

 of the spruce (Figs. 191 and 192). The young wood cylinder of 

 the spruce during the first year is therefore similar to that of a 

 fern like the maidenhair in having leaf gaps where portions of 

 the wood and phloem cylinder pass out to form a leaf trace. 

 This persistence of a fern characteristic in the stem structure of 



