34i 
Barber Cupressi noxylon vec tense. 
is taken from root, stem or branch. In the rings of a Coni- 
ferous stem, according to Mohl \ there is a gradual decrease 
in the radial diameter of the cells from the first tracheides 
of the ring to the last, accompanied by an increase in the 
thickness of the walls. In a root-ring, on the other hand, 
a number of layers of wide spring-elements are succeeded 
suddenly by a band of flattened thick-walled summer-cells 
which terminate the ring. This difference is explained in 
the following way. In a wide ring, whether in stem, branch 
or root, there are three distinct zones which differ as regards 
the form and size of their cells — an inner layer of wide 
square cells, a middle zone of polygonal, usually hexagonal 
cells, and an outer zone of typical summer-cells which are 
again more or less rectangular. Stems generally have wider 
rings than branches or roots, and all three layers are met 
with in them. In branches the inner layer is variable, and 
in thin rings is frequently absent. In roots on the contrary 
it is the middle layer which varies, and in thin rings it is 
usually wanting. 
The thin rings which characterize smaller roots and 
branches are thus seen to be very different in appearance. 
In branches a set of hexagonal cells passes gradually into 
the thick, flat summer-cells ; in roots wide, square tracheides 
are followed without transition by the flatter layer, which, 
in this case, is often reduced to only two or three rows 
of cells. 
On applying these facts to our fossil sections we note 
that they can with little difficulty be divided into two sets 
(Figs. 2 and 3). In one of these, which I have called branch (1) 
and branch (2), the cells of the inner layer are polygonal and 
pass gradually outwards to from 2-12-20 summer cells. In the 
other specimens, while in places there are gradual transitions, 
many parts show a sudden passage from wide, frequently 
squared cells, to from 1 -2-4-6 flat dark tracheides. These 
I have called root (1) and root (2). It seems therefore probable 
1 Mohl, Einige anat.und physiol. Bemerkungen iiber das Holz der Baumwurzel, 
