5 



THE ANATOMY OF WOODY PLANTS 



the higher Coniferales. Fig. 37 illustrates the distribution of the 

 wood parenchyma in those dicotyledons in which the condition is 

 diffuse. In a is shown a transverse view of the secondary wood in 

 the black walnut (Juglans nigra). The distribution of the storage 

 cells is made clear by the outlining of their walls in solid black. 

 In b the same wood is depicted in longitudinal radial aspect, and the 

 nature and distribution of the parenchymatous elements become 

 doubly clear. A fact not without interest from the evolutionary 



FIG. 37. Diffuse parenchyma in Juglans. Explanation in the text 



standpoint is the uniform distribution of parenchyma after this 

 fashion in whole natural orders of dicotyledons. For example, in 

 the Juglandaceae, Betulaceae, Fagaceae, Ebenaceae, Ericaceae, 

 etc., the disposition of the longitudinal food-storing cells of the 

 wood is entirely of the manner designated above as diffuse. 



In other orders of dicotyledons, particularly those which are 

 with some degree of unanimity assigned by systematists to a high 

 position, a strikingly different mode of parenchymatous arrange- 

 ment is found. This is notably the case in the Compositae, 

 Verbenaceae, Oleaceae, etc. The situation in this type of distribu- 

 tion of parenchyma can be clearly indicated by reference to the 

 ash. Fig. 380 shows the grouping of the parenchyma at the end 



