736 PROFESSOR W. C0. WILLIAMSON AND DR. D. H. SCOTT ON THE 
The roots occur on all sides of the stem, a point of some importance with reference 
to the habit of the plant. Longitudinal sections show that they were scattered quite 
irregularly, occurring both on nodes and internodes ; their position shows no relation 
to that of the leaves.* We arrive, then, at the following conclusions :— 
1. The stem of Lyginodendron bore numerous adventitious roots of endogenous 
origin, which occurred both at the nodes, and on the internodes. 
2. These adventitious roots are identical with the fossils previously described under 
the name of Kaloxylon Hookeri. 
2. Primary Structure of the Root. 
The organization of Kaloxylon Hookeri has been fully described and illustrated in 
former memoirs.t Now, however, that its true nature is known, it becomes necessary 
to reconsider its structure in the light of our present knowledge. 
When once the right clue has been obtained, there is no difficulty in recognizing 
all the specimens of Kaloxylon as roots. This is evident on inspecting the various 
figures in Memoirs VII. and XIII, or our own photographs 11-15. Following our 
usual course, we will first consider the primary structure of the root, and then the 
changes due to cambial activity. 
The central cylinder of the root, before the commencement of secondary thickening 
has a perfectly typical radial structure, the number of xylem-groups varying from 
8 down to 8, or possibly even 2 in the finest rootlets. The smallest primary 
tracheides are invariably at the peripheral ends of the radiating xylem-strands (see 
Plate 20, photograph 11 and Plate 25, fig. 20). That these peripheral elements really 
represent the protoxylem is preved by radial longitudinal sections, such as that shown 
in fig. 19. This section passes exactly through one of the primary strands of wood, 
and shows a narrow spiral tracheide, px, at its outer limit. Towards the interior the 
tracheides become rapidly wider, and here their walls are pitted. The border of 
the pits is sometimes well preserved. The absolute dimensions of the more central 
tracheides vary greatly, the diameter ranging from ‘036 to ‘09 millim. in different 
specimens. 
Among the tracheides there is a considerable amount of conjunctive parenchyma, 
which is relatively most abundant in the largest steles. Sometimes this tissue 
separates the xylem-groups from one another (see photograph 11), sometimes it 
is irregularly scattered among the tracheides (see photograph 12). The conjunctive 
parenchyma consists of square-ended prismatic cells (see fig. 19). This combination 
of tracheides and parenchyma gives a highly characteristic appearance to the trans- 
verse sections of the larger steles. The parenchymatous bands sometimes extend to the 
* The most important preparations for the connection between root and stem are the following :— 
C.N. 1144, A.; 1144, B.; 1147; 1148; 1883; 1885; 1885, A., B., and C. (same specimen) ; 1885, 
I., K., and L. (same specimen); and 1981. 
¢ Wiuiamson, “ Organization,” Parts VII. and XIII, 
