198 CALAMOPITYEAE [CH. 



intervals ; the one branch, that on the anodic side [turned towards 

 the course of the genetic spiral], becomes the leaf-trace and passes 

 out, while the other continues its course up the stem as a reparatory 

 strand, until the next leaf of the orthostichy has to be supplied 1 .' 

 The secondary xylem consists almost entirely of tracheids with 

 3 4 rows of pits on the radial walls and medullary rays usually 

 one cell broad varying in depth from 1 or 2 to 16 or more cells. 

 A characteristic feature of the secondary xylem is the occurrence 

 on its inner face of numerous short and broad tracheae similar 

 to the still larger tracheae in the primary stele of Megaloxylon 2 . 

 Nothing is known as to the behaviour of the leaf-trace in the 

 extrastelar region, but the fact that an outgoing trace was found 

 to have two protoxylems points to a subdivision similar to that 

 of the foliar bundles of Calamopitys Saturni. A well-marked 

 difference between Eristophyton fasciculare and Calamopitys and 

 Lyginopteris is the more compact structure of the secondary wood ; 

 it is pycnoxylic and not manoxylic. Prof. Zalessky in criticising 

 the use of the generic title Calamopitys puts forward several 

 arguments in support of his institution of a new designation: 

 (i) the primary xylem strands of Eristophyton are not confined 

 to the periphery of the pith as is the case in Calamopitys Saturni, 

 though he speaks of one leaf-trace in the latter species separated 

 by several layers of cells from the xylem-cylinder ; (ii) some of 

 the pith-cells have thick walls and dark contents in distinction 

 to the homogeneous parenchyma of Calamopitys, a feature of 

 little importance; (iii) the difference in the structure of the 

 secondary wood already alluded to, though this loses some of 

 its significance by the occurrence of narrower rays, more like 

 those of Eristophyton, in C. annularis ; (iv) the more elliptical 

 and broader pits in the secondary tracheids in place of the more 

 regular hexagonal form in Calamopitys. While admitting a 

 certain degree of relationship between the two types, Zalessky 

 asserts that as yet we have insufficient evidence to justify their 

 generic union. Scott 3 maintains that Zalessky does not attach 

 sufficient weight to the form and mesarch structure of the primary 

 xylem bundles as a feature common to both genera. 



1 Scott (02) p. 336. 2 Page 175. 



3 Scott (12) p. 1027. 



