322 CALAMITES. [CH. 



to the stem-wood a curiously characteristic appearance \ as if 

 the xylem elements had been pushed aside and contorted by 

 the pressure of the outgoing member. A tangential section 

 through a Pine stem^ in the region of a lateral branch presents 

 precisely the same features as in Calamites. The branches are 

 given off from the stem immediately above a node and usually 

 between two outgoing leaf- trace bundles. 



Specimens of pith-casts occasionally present the appearance 

 of a curved and rapidly tapered ram's horn, and the narrow 

 end of such a cast is sometimes found in contact with the node 

 of another cast. This juxtaposition of casts is shown unusually 

 well in fig. 82. In some of the published restorations of Calamites 

 the plant is represented as having thick branches attached to 

 the main stem by little more than a point. Williamson^ clearly 

 explained this apparently unusual and indeed physically impos- 

 sible method of branching, by means of sections of petrified stems. 

 The branches seen in fig. 82 are of course pith-casts, and in the 

 living plant the pith of each branch was surrounded by a mass 

 of secondary wood developed from as many primary groups 

 of xylem as there are grooves on the surface of the cast, each 

 of the grooves on an internode corresponding to the projecting 

 edge of a xylem group. At the junction of one branch with 

 another the pith was much narrower and the enclosing wood 

 thicker, so that the tapered ends of the cast merely show the 

 continuity by a narrow union between the pith-cavities of 

 different branches. Most probably the casts of fig. 82 are those 

 of a branched rhizome which grew underground, giving off 

 aerial shoots and adventitious roots. There is a fairly close 

 resemblance between the Calamite casts of fig. 82 and a stout 

 branching rhizome of a Bamboo, e.g. Bamhusa arundinacea 

 Willd. ; it is not surprising that the earlier writers looked upon 

 the Calamite as a reed-like plant. 



Before leaving the consideration of stem structures there 



1 Vide Williamson (71), PL xxviii. fig. 38; (Tl^), PI. iv. fig. 15; (78), PI. xxi. 

 figs. 26—28. Williamson and Scott (94), PI. lxxii. figs. 5 and 6. Kenault (93), 

 PI. xLv. figs. 4—6, etc. Felix (96), PI. iv. figs. 2 and 3. 



2 Strasburger (91), PL ii. fig. 40. 



3 Williamson (78). 



