GNETALES 



363 



and the dicotyledons were in the first instance related to the 

 appendages, whether branch, leaf, or root. While, however, 

 the prominent masses of radial storage parenchyma which dis- 

 tinguish the groups under consideration are not primarily related 

 to the appendages, they become somewhat definitely limited to 

 this position in many forms, and even in the Gnetales themselves 

 are more strongly developed in connection with lateral organs. 



We may next turn 

 to the anatomical 

 organization of the 

 genus Gnetum. Fig. 261 

 illustrates the general 

 structure of the stem 

 in this genus as exem- 

 plified by a young stem 

 of Gnetum scandens. 

 The appearance is very 

 similar to that of a 

 dicotyledonous vine 

 like Clematis or Vitis. 

 Extremely prominent 

 large rays separate the 

 woody cylinder into 

 distinct fibro vascular 

 strands. The large rays of Gnetum are distinguished from the corre- 

 sponding features of organization in Ephedra by two important 

 details. In the first place, like those of the dicotyledonous climbers 

 cited above, they extend broadly to the pith and do not appear first 

 as narrow rudiments which are widened as they pass toward the out- 

 side of the woody cylinder. Secondly, the broad rays of Gnetum 

 are in the stem usually entirely homogeneous; that is, they contain 

 no distinct vestiges of fibrous and vascular structures such as 

 appear in the broad radial storage bands of Ephedra, although 

 in types like G. scandens the broad rays of the stem are not obviously 

 derived from compounding of aggregations of rays and longitudinal 

 elements of the wood. Investigations on the part of Professor 

 W. P. Thompson as yet unpublished seem to make it clear, how- 



FIG. 261. Transverse section of young stem of 

 Gnetum scandens. 



