n6 



THE ANATOMY OF WOODY PLANTS 



protoplasm and starch. In the middle region of the figure a file 

 of parenchyma cells is present. To the left of the middle line the 

 sieve elements show the delicate protoplasmic lining which char- 

 acterizes them in the functional condition. The radial parenchyma 

 is also entirely in a living condition, although the marginal cells 

 are differentiated by the absence of the starch contents found in the 



FIG. 89. Tangential section through the phloem. Explanation in the text 



central region of the ray structure. The callus in both sieve tubes 

 and marginal cells is here conspicuous by its absence. 



A somewhat complicated condition of the phloem has purposely 

 been chosen in the case of the coniferous gymnosperms, because 

 there is good reason to believe that in this group, which is a decadent 

 one, the more elaborately organized condition is antecedent to that 

 marked by a greater degree of simplicity. On the whole, the pine 

 and its allies represent the most highly differentiated structure of the 

 phloem in the group. In the Cupressineae, Taxodineae, Araucari- 

 neae, Podocarpineae, and Taxineae the radial structures of the 

 phloem show a marked degree of simplification as compared with 



