362 



THE ANATOMY OF WOODY PLANTS 



diffuse wood parenchyma) found storage in the woody tissues 

 of the axis. 



It will be obvious from the facts brought forward in the pre- 

 ceding paragraph that diffuse and abundant wood parenchyma, 

 vessels, and large rays are features which are intimately corre- 

 lated in the organization of the woods of the Gnetales and the 

 dicotyledons. That the situation portrayed is correct from the 



evolutionary stand- 

 point is rendered 

 clear by a condi- 

 tion presented not 

 infrequently in the 

 wood of our living 

 species of Pinus. 

 Fig. 260 illustrates 

 an interesting ab- 

 normal feature 

 which is often found 

 in the wood of the 

 white pine. The 

 annual rings are 

 strongly depressed 

 locally, and in these 

 regions the rays of 

 the wood are 



unusually abundant, or, in other words, are clustered or aggregated. 

 Since in the genus Pinus wood parenchyma is absent a feature, 

 as has been indicated in earlier pages, definitely correlated with 

 its primitive phylogenetic position the clustering of the rays, 

 particularly in the absence of vessels, is of no evolutionary signifi- 

 cance. This, of course, is primarily the result of the absence of 

 the later acquired capacity of producing the longitudinal paren- 

 chyma so necessary for the fusion of the aggregation of rays into 

 large and homogeneous storage units. It may further be remarked 

 in a general way that there is no evidence to show that the large 

 masses of storage parenchyma which are so striking a feature 

 of the organization of the woody cylinder of both the Gnetales 



FIG. 260. Aggregate ray from Pinus Strobus 



