388 Chandler . — On the Arrangement of the Vascular Strands 
the branching of the stem at this level. The branching takes place into 
two such equal parts that one is inclined to infer that true dichotomy must 
obtain, though this point has not been settled. Fig. 192 represents the 
stage at which the three cauline strands have completely united ; the 
separation of the leaf-trace is also seen to be taking place. Before 
the latter is effected, however, the cauline system appears, as we pass 
upwards, to be ‘pinched in’ at its centre (Fig. 193). The constriction 
is completed immediately after the leaf-trace leaves the vascular system, 
with the result that we have the appearance of two nearly independent 
solenostelic structures (Fig. 194). In one plant examined, the two rings 
were completely separate before the stem actually bifurcated (Fig. 196), 
though the usual state of affairs is for the stem to branch immediately the 
separation of the vascular rings seems about to occur. 
Each of the two branches will therefore be seen to possess at its base 
a vascular structure, which, in transverse section, presents a typical soleno- 
stelic appearance, such as occasionally occurs in the stem before bifurcation 
takes place. As in the latter case, however, the condition is a very transitory 
one, the complete rings soon breaking at corresponding points (Fig. 195) in 
preparation for the insertion of a pair of leaf-strands. From this point 
onwards, the vascular organization resembles, in main outline, that of 
the stem before the region of branching, and will be described at no further 
length. 
The method of branching in Nothochlaena sinuata closely resembles 
that occurring in Schizaea dichotoma and Pteris incisa , as described by 
Boodle \ and Tansley and Lulham 1 2 respectively. In Pteris the processes 
involved in the branching are considerably more complex than those 
obtaining in Schizaea or Nothochlaena , but in all three cases we have the 
occurrence of dichotomy accompanied by the formation of a median 
leaf-trace. 
As shown in Figs. 187, 192, 194, the ground-tissue in all but the 
youngest plants consists of two sharply contrasting portions. A narrow 
band immediately outside the outer endodermis is composed of soft-walled 
cells, as is the whole of the portion surrounded by the almost complete 
vascular ring. The peripheral part, however, is composed of small cells, 
the thick walls of which are coloured a deep reddish-brown, contrasting in 
a striking manner with the colourless thin-walled parenchyma and with the 
vascular tissue. 
1 Comparative anatomy of the Hymenophyllaceae, Schizaeaceae, and Gleicheniaceae. IV. Fur- 
ther observations on Schizaea. Annals of Botany, xvii. 
2 The vascular system of the rhizome and leaf-trace of Pteris aquilina, L., &c. New 
Phytologist, iii, 1904. 
