STIGMARIA. 275 



Sections of the appendages in any desired direction are obtained in 

 the greatest abundance by slicing the calcareous nodules from the coal- 

 measures. The appendages traverse these nodules on all sides, forming 

 with fragments of fern-leaves much the larger portion of their contents. 

 Here too it is extremely rare to find all the tissues preserved alike. In 

 the following remarks we will first consider the usual state of the specimens. 

 A thin peripheral cylinder of parenchyma surrounds a broad cavity filled 

 with a structureless mass of matter, in which lies a second similar hollow 

 cylinder inclosing the wood-strand. The broad tube of the outer cylinder, 

 which is generally circular on the transverse section, is often squeezed to- 

 gether, or even bent and folded in a great variety of ways, especially when 

 the appendages lie several of them close together or have had to force 

 themselves through narrow orifices. The inner cylinder often lies free in the 

 centre of the cavity of the outer, or it may be connected with its wall by 

 means of a bridge-like plate of parenchyma which has been preserved *. In 

 other cases again it is quite excentric and rests against the wall of the outer 

 cylinder, having evidently subsided into this position after the destruction 

 of the surrounding tissue. The inner cylinder too is by no means entirely 

 filled by the wood-strand, which touches it only at one point. The two are 

 separated everywhere else by a nearly circular intervening space, which, 

 moderate in its dimensions, is broadest exactly opposite the point of contact 

 and decreases from this point in both directions. It has been already stated 

 on p. 264 that the appendages sometimes branch dichotomously. I have 

 seen in Williamson's collection several sections passing exactly through the 

 place of bifurcation. Then the xylem-strand separates by median division 

 into two lateral halves, which at first lie side by side in the expanded ovoid 

 inner cylinder but afterwards move further apart, while a bridge of paren- 

 chyma makes its appearance between them and divide^ the space into two 

 distinct compartments. Sections 2 a little higher up show the two com- 

 partments moved away from one another, and developed into separate 

 inner cylinders, which in many cases are still connected by traces of 

 parenchyma, such as might easily have been preserved in the narrow 

 intervening space. 



Williamson 3 has given a figure of an appendage of the normal kind, 

 but with all its tissues preserved. Here the space between the outer and 

 inner cylinder is filled with a layer of thin-walled tissue with its boundaries 

 on both sides sharply defined. The transverse section 4 also is of quite 

 similar characters ; only its outer cylinder is unusually large and shows two 

 distinct cell-layers, the inner one of which is remarkable for the thickness 



1 Williamson (6), t. 13 and (1), XI, t. 53, f. 16. a Williamson (6) r t. 11. 3 William- 



son (1), xr, t. 53, f. 15. * Williamson (6), t. 9. 



T 2 



