Bancroft.—On the Xylem Elements of the Pteridophyta. 753 
may be the result of contraction and splitting of the membrane during 
drying or decay.’ In view of later work it would seem that Professor 
Seward’s second suggestion is the more probable explanation of the appa¬ 
rent connexions. 
An examination of a fairly representative collection of fossil slides 
resulted in the discovery of two excellent longitudinal sections—one of 
Stigmaria jicoides and one of Sphenophylhtm plurifoliatum —showing the 
middle lamella distinctly (Text-fig. 3, a and b). 
Text-fig. 3. (a) Stigmaria Jicoides. Longitudinal section of xylem. (From a photograph.) 
( b ) Sphenophyllum plurifoliatum. Longitudinal section of xylem. (From a photograph.) (The 
arrows in both cases point to the middle lamella.) 
In S. ficoides the lamella appears as a double line. This is probably 
due to the fact that the two edges of a thick section are seen, the section 
being also somewhat oblique, as shown by the bars, and the fact that one 
line, representing one edge of the arc of lamella, is at a lower focus than the 
other. 1 
To return to the recent forms, in a fair number of cases longitudinal 
hand-sections were obtained in which it was clear that a series of scalariform 
bars must have been cut through twice. But the sections of the bars did 
not fall away from one another, as would have been the case if Gwynne- 
Vaughan’s view of the absence of a connecting membrane were correct. In 
fact, it would have been impossible to obtain such a section by hand as that 
shown in PI. LVI, Fig. 4. 
1 Since the above was sent to press, the writer finds that Williamson and Scott figured the 
middle lamella in Calamites in their paper ‘ Further Observations on the Structure of the Fossil 
Plants of the Coal Measures/ Part I, p. 883, PI. 78, Fig. 9 (Phil. Trans. B., vol. clxxxv, 1894). 
