330 DESCRIPTIVE CATALOGUE 



seasons, however, it is difficult to suggest any cause for their 

 appearance. They are far too regular to be compared with the 

 very erratic courses sometimes followed by the anomalously 

 formed secondary bundles in Dracwna *, though Dracaena seems 

 to be the only plant with which even comparison can be 

 suggested. 



De Bary (1884, pp. 471 et scg.) notes that in woods there is 

 very frequently a torsion of the. longitudinal elements, so that 

 they do not run quite vertically, and he mentions that this 

 torsion is right-handed in ^Esculus hippocastanum and left- 

 handed in Populus jtyranii'lalis. He also says that " in main- 

 lands of trees, as Pines and Firs, the direction of the fibres 

 changes, becoming reversed after a number of similarly inclined 

 layers." But the amount of torsion in the chestnut or pine 

 Avoods is not comparable in degree to that in the fossil, though 

 it is not impossible that it may be to some extent similar in 

 kind, for, as was pointed out in the description (p. 326), there 

 seem to be grounds for thinking that the successive cylinders 

 of the fossil are formed from one cambium. If this is so, tlio 

 cambium direction must have turned over at right angles to the 

 normal growth of the cylinders at remarkably regular intervals. 

 I can offer no suggestion as to why it should have done this. 



As in living Cycads the " girdles " of the leaf-traces, which 

 run half-way round the stem, are so conspicuous a feature, it is 

 noteworthy that in the fossil the horizontally running cylinders 

 disregard the leaf-trace (text-fig. 109, B, It.). It appears pro- 

 bable that these cylinders have nothing to do with the leaf- 

 traces in the fossil, though it is not impossible that there may 

 be some phylogenetic connection between them and the girdles 

 in living Cycads. 



Finally, the inclusion of this plant in the Cycadophyta is self- 

 evident, but while in some respects it is like both Bennettites 

 arid Cycadeoidea, the fossil represents a new genus, of which 

 the degree of remoteness from the known Mesozoic Cycado- 

 phyta cannot be estimated without some knowledge of its 

 fructification. 



* I am indebted to Prof. Oliver for Dractsna material and for calling 

 my attention to the peculiarity of the bundle-courses in its secondary 

 wood. 



