330 Bower. — On the Structure of the Axis 
living forms ; as an example Astromyelon Williamsonis may 
be taken 1 . Here the cells bordering on the lacunae are so 
well preserved, and the whole nature of the tissue so similar 
to what is commonly found in living aquatic plants which 
show schizogenetic spaces, that the conclusion is justified that 
the lacunae existed in the living state, with essentially similar 
characters to those now seen in the fossil. 
As a second example Rhizonium lacunosum may be cited 2 . 
Here the cortex has clearly been lacunar, as in Astromyelon , 
but many of the trabeculae of tissue are broken, and the 
question arises whether they were broken during life or sub- 
sequently ; it seems not improbable from the appearance of 
the section represented in the figure which has been quoted, 
that the rupture was made after death. 
It will hardly be necessary to remark that the most difficult 
cases for decision will be those where the cavities are lysi- 
genetic ; to draw the line between the natural destruction of 
cells and tissues in the normal life of the plant, and the dis- 
organization of the softer tissues after death, but before 
complete fossilization, will clearly demand the most careful 
examination of well-preserved specimens. 
It is well known that large gaps are commonly present in 
the tissues of Lepidodendron , and they are found, not only in 
the normal stems and Stigmarian roots, but also in the axis 
of the strobilus. 
In transverse sections of Stigmarian rootlets, two spaces are 
commonly found : an outer large space in the cortex, in which 
the central vascular strand is suspended, being sometimes 
attached by a bridge of tissue to the peripheral band of 
cortex 3 , and an inner space immediately surrounding the 
strand of xylem. Let us consider first the outer of these 
spaces, viz. that in the cortex. Professor Williamson gives 
1 Organization of Fossil Plants of the Coal Measures. Williamson, Phil. Trans., 
Pt. II, 1883, Pis. 27-30. 
2 Williamson, Phil. Trans., vol. 180 (1889, B. PI. Ill, Fig. 23). 
8 Compare Williamson, Monograph on Stigmaria Jicoides (Palaeontographical 
Society, 1886). PI. XIII, Fig. 79. 
