HETERANGIUM 405 



recognised, and as all subsequent research has confirmed, 

 the evidence of consanguinity is clear and convincing. 



The primary wood in Heterangium is composed 

 throughout of irregular anastomosing groups of tracheae, 

 interspersed with strands of conjunctive parenchyma 



Fig. 156. — Heterangium Grievii. Part of transverse section, from outer part of stele, 

 showing a primary xylem-strand and adjacent tissues, px, protoxylem of strand ; 

 -*-, centripetal, jr 1 , centrifugal, primary wood ; nix, metaxylem, c.p, conjunctive 

 parenchyma ; .r 2 , secondary wood ; cb, cambium ; pit 1 -, phloem. X 135. Phil. 

 Trans., W. and S. Will. Coll. 1293. 



(Figs. 154 and 155, x). As a rule, the tracheae are 

 more abundant than the parenchyma, and even where 

 the reverse is the case, there is never any aggregation 

 of the cellular tissue to form a pith. The structure 

 of the primary wood is not, however, uniform in all 

 its parts. Around its periphery, definite clusters . of 

 tracheides can be distinguished, each of which agrees 



