6 4 
Cormack. — On a Cambial 
Famintzin, Sadebeck, Van Tieghem and Douliot, Muller, and 
Strasburger 1 . 
Thus this order, with its one genus and diagrammatic 
regularity of structure, has come to be regarded as one of the 
best understood groups of plants. 
Buried in more recent strata are found fossils whose close 
relationship with modern Equisetaceae is not called in 
question ; but the Carboniferous, Permian, and Triassic 
formations contain a group of fossils, the Calamitae, which 
some palaeobotanists would place bodily beside Equisetaceae, 
but which certain others seek to divide into two classes by 
removing one section and placing it among the Phanerogams. 
The problem can best be approached by such a brief 
description of Calamitae showing minute structure, as is 
required for the purpose of this paper. 
In a transverse section passing through an internode of 
one of these stems, there is seen a ring of woody wedges 
united by inter-fascicular tissue. The angle of each wedge is 
directed towards the centre of the stem, and each abuts on a 
cavity of its own. 
Within this first ring is a second, composed of parenchy- 
matous cells which form the outer limit of a central cavity. 
Such is the appearance commonly presented in transverse 
section ; but in a few cases a peripheral ring of the rind has 
also been preserved (see Williamson’s 2 figure ; and Plate VI, 
Fig. 1 1). 
Tangential sections through the woody wedges show that 
these wedges represent strands passing longitudinally through 
the internodes. The strands belonging to adjacent inter- 
nodes alternate — in most types — but are united into one 
continuous system ; for each strand bifurcates in the node, so 
as to give an arm to each of the two strands lying to the 
right and left of it in the adjacent internode. Thus the 
commissures in the node form a zig-zag line similar to that 
found in the Equisetaceae. 
1 See list at end of paper. 
2 Phil. Trans., 1871, Plate XXIII, Fig. 9. 
