148 



THE ANATOMY OF WOODY PLANTS 



to the genus Larix, while the actual photomicrograms illustrate the 

 fir (Abies). In the first of these (Fig. 104) is depicted the root in a 

 younger stage of 'development. The general situation is clearly 

 identical with that in the larch, since the central region of the root 

 is sharply set off from the cortex by the presence of a well-marked 

 endodermis, a structure, by the way, not found in any organ of the 

 genus but the root. In the central cylinder may be seen the broad 



FIG. 103. Transverse section of an older root of the American larch, 

 tion of this and preceding figure in the text. 



Explana- 



encircling pericycle, bounding the primary phloem above and below. 

 Within the first-formed phloem lies the mass of primary wood, not 

 as yet completed in the central region, and thus clearly indicating 

 the centripetal order of development of the elements of that portion 

 of the woody structures. In the midst of the primary xylem is 

 situated a resin canal which is not yet fully developed. The singu- 

 larity of number and the axial position of the secretory canal 

 furnish practically the only features of distinction from the cor- 

 responding structures in the case of the larch, where the plural 



