882 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
(C.N. 1554, from which photograph 6, on Plate 72 was taken), we measured two 
trachez, the lengths of which were almost the same, namely 4°1 and 42 millims. This 
is just equal to the maximum length of the tracheides in Pinus.* In the fascicular 
wood the trachese run approximately vertically, with only trifling curvatures. 
We have found it a very general rule that the pits in the secondary trachez are 
limited to their radial walls. This statement is based on the evidence of all the 
tangential sections which are sufficiently well-preserved to show the structure in detail. 
The absence of pits on the tangential walls cannot be merely apparent, or due to 
imperfect preservation, for the same tangential sections, which show no pits in surface 
view, present quite obvious pits, seen in section, on the radial walls of the trachez 
(see Plate 78, figs. 8 and 9), while radial sections of the same specimens, show the pits 
in surface view with perfect clearness (see Plate 78, figs. 7 and 10).t We regard the 
establishment of this fact as of considerable interest, for it indicates that the 
inechanism for the passage of sap through the wood of Calamites was of the same kind 
as that existing in recent Conifers. Such a character is, of course, of no systematic 
value, as is shown by the well-known case of Drimys among the Dicotyledons.{ 
It is only in the most internal part of the fascicular wood, immediately outside the 
canal, that we find tangential pits on the trachez. They were either limited to the 
primary xylem, or at most extended toa few of the first-formed secondary layers (see 
Plate 80, fig. 21). As already mentioned, the peculiar short-celled wood at the nodes 
has pits on all surfaces of its elements, but we have already given reasons for 
regarding this wood as primary. 
The pits on the radial walls are sometimes of the scalariform type, that is, they are 
transversely elongated, so as to extend across the whole width of the wall; in other 
cases they are shorter, having an elliptical outline. More than one row of pits may be 
present on the same radial wall. In some radial sections it appears that the scalariform 
pitting is limited to the more internal trachez, sometimes even to those which may be 
regarded as primary, while all the pits seen on the more external trachez are of the 
shorter form. This, however, is not w constant rule. For example, in the largest 
specimen of which we have examined sections,§ the scalariform type of thickening 
prevails in all parts of the wood, which is 2 inches thick, though tracheze with shorter 
pits are seen here and there. As the nature of the pitting may vary in different parts 
of the same trachea, we attach little inportance to these differences. They probably 
depend in part on the relative positions of the tracheze. Where the elements in two 
adjacent radial rows correspond, so as to be in contact with each other by their entire 
radial surfaces, we geuerally find scalariform pitting. Where, however, the elements 
* See pz Bary, loc. ctt., p. 506. 
+ The preparations on which these statements are chiefly based are, C.N. 20, 20a and nz, 21, 22, 
65-68, 83-87, 88-91, 130* and 131*, and 137*, 138*, 1554, and 1937. 
+ See Straspurcer, ‘ Histologische Beitrage,’ vol. 3, p. 161. 
§ The radial section is C.N, 80. See Wiittamson, “ Organization,” Part TX., Plate 20. 
