180 PROF. W. C. WILLIAMSON ON THE STRUCTURE 



ditional study of the older fossil plants, including those 

 of the Oolitic age, makes plain the difficulty, if not the 

 impossibility, of identifying them exactly with living types. 

 Special organs may and do exhibit close resemblances ; 

 but the general combinations are frequently different. In 

 this respect the recent Cycads retain something of the 

 features of the more ancient vegetation. In their stems 

 we find the scalariform and annular vessels of the Acro- 

 gens side by side with the gymnospermatous inflorescence 

 and the Araucarian forms of glandular tissue linking them 

 with Conifers, whilst in one aberrant genus (Stangeria) we 

 have the stems and cones of Cycads combined with the 

 foliage and nervures of a true Fern. The differentiation 

 which has been so complete in other plants appears to 

 have remained unaccomplished in the Cycadese. 



Various attempts have been made to restore the Cala- 

 mite, as well as the other plants of the Coal-measures ; 

 and though such attempts have been hitherto, and still 

 are, premature, they are not altogether useless, since they 

 mark the successive stages of progress towards truth. In 

 the instance of the Calamites, we have especially the re- 

 storations of M. Deslongchamps (given in the ^ World 

 before the Deluge^ of Louis Figuier) and those of Dr. 

 Dawson (Acadian Geology, 2nd ed. p. 442) . The former 

 represents the plant as giving off from its central stem large 

 bushy branches, like those of some modern Araucarias. To 

 this idea the structure of the woody zone affords no support. 

 If any large branches had sprung from the main stem, the 

 structure of this zone would have shown unmistakable 

 evidences of the fact in the lateral deflection of large 

 masses of vascular tissue. But I see no evidence of such 

 large deflections. We have deflections on a small scale; 

 but the diameter of the largest and thickest of these di- 

 vergent vascular bundles never exceeds the breadth of one 

 of the longitudinal ribs of a Calamite ; hence the vascular 



