4 8 



THE ANATOMY OF WOODY PLANTS 



normal structure of the wood in the vegetative stem, but is ordina- 

 rily clearly and sometimes even abundantly present in the diffuse 

 condition in regions which are conservative of ancestral characteris- 

 tics, such as the root, cone axis, etc. It may, moreover, be easily 

 recalled as a consequence of experimental procedure. It is accord- 

 ingly clear that, from the evolutionary standpoint at any rate, con- 

 siderable care is necessary in deciding as to the primitive presence 

 or absence of parenchymatous elements in the woody tissues of the 

 conifers. 



A B C 



FIG. 36. Diffuse parenchyma in a coniferous wood. Explanation in the text 



Fig. 36 shows the topography of the diffuse condition of paren- 

 chyma in coniferous woods in three dimensions. In a is seen the 

 transverse view of a wood of this type. The longitudinal storage 

 elements, or wood parenchyma, are represented with heavy black 

 walls to bring out by contrast their distribution in the general 

 structure and at the same time the frequent chemical difference 

 of then- walls from the tracheary tissues proper. In b appears 

 the tangential aspect of the storage elements, in which they present 

 themselves in the greatest breadth and on the whole show most 

 clearly by pits their relation to other elements of the wood. In the 

 case of c these important elements of wood structure are revealed in 

 the radial aspect, and their diffuse disposition is as apparent as in 

 the transverse plane of section. 



