of the Fossil Plants of the genus Sigillaria. 125 
one and the same plant? ‘‘ The hypothesis involved in this question,” 
says its author, ‘‘ appears, however, to have little probability in its favour, 
in consequence of there being none of the prolongations on the outer 
part of the vascular cylinder of Anabathra which are visible on the cor- 
responding part of Lepidodendron.” The prolongations here alluded to, 
are those portions of the leaf cords which are on the point of curving off 
from the cylinder, to the margin of which they give a sinuous appear- 
ance. Mr Witham’s transverse sections of Anabathra certainly do not 
shew any sinuosities. Brongniart’s objection is, therefore, so far a valid 
one ; but it seems to me that, before Lepidodendron can be considered as 
the branch of Anabathra, there is required to be known an example of 
a Dicotyledonous tree having young branches without any radially ar- 
ranged ligneous tissue. 
Sigillaria elegans possesses in its anatomy a peculiarity of considerable 
interest, in a physiological point of view: it is furnished with a medul- 
lary sheath, which, there is strong reason to believe, existed, to a certain 
degree, independently of the ligneous zone. But whatever doubt might 
stand in the way of such a peculiarity possessing itself of our entire con- 
yiction, so far as Sigiliaria is concerned, it is clearly demonstrated by 
what is observable in Lepidodendron and Anabathra, inasmuch as, in the 
former, the vascular cylinder has performed its function without the pre- 
sence of the ligneous zone of the latter: add to this, that, in Anabathra, 
although these two parts are in immediate contact with each other, the 
differences which have been pointed out in their respective tissues, further 
prove that they represent independent systems. It will now be seen on 
what grounds the distinction has been made in this paper between the 
vascular and the ligneous part of the fossils which have been mentioned. 
With the materials which we now possess connected with the internal 
structure of co-existing forms, it will readily be admitted, that we are 
better prepared to commence our proposed examination of the histology 
of Stigmaria. 
Lindley and Hutton were the first to make us acquainted with the 
anatomy of this fossil, and, subsequently, Brongniart and Morris have 
each contributed towards elucidating it. 
A transverse section of a Stigmaria having its tissue preserved, usually 
exhibits the appearances shewn in figure 1, Plate V. The letter d refers 
to a broad zone filled with mineral matter which has replaced the original 
(cellular) tissue of the plant: the wedge-shaped bundles marked a 8, are 
composed of very elongated hexagonal or quadrilateral tubes, whose walls 
are marked with transverse lines or bars, in general parallel to each other, 
but occasionally approximating at certain points, so as to produce a re- 
ticulated appearance (Brongniart): these tubes are arranged in lines 
radiating from the centre of the fossil : ¢ refers to spaces which separate 
the bundles from each other ; they are now filled with the same mineral 
substance as that of the outer zone, but there is no doubt of their having 
been originally occupied with cellular tissue: the part marked ¢ is also 
