in the ‘ Seedlings ’ of Certain Leptosporangiate Ferns . 399 
favourable sections, however, it was seen that its cells were not in seriation 
with the pericycle cells, thus confirming a similar statement made by Seward 
and Ford with regard to T. hymenophylloides. 
DlCKSONIA ANTARCTICA, Labilh 
The development of the vascular system in Cyatheaceae has received 
but little attention. As far as the writer is aware, the only account of the 
transitional changes is that occurring in Gwynne-Vaughan’s second paper 
on Solenostelic Ferns *, in which the author describes the young stages 
of Alsophila excelsa . In addition to the latter plant, the writer has had 
the opportunity of examining Dicksonia antarctica. 
The vascular strand of the primary root is of the normal diarch type, 
resembling that of Alsophila excelsa in being extremely small. The 
vascular elements, however, especially the sieve-tubes, are well differen- 
tiated. The usual transition to the solid protostele occurs, and a single 
parenchyma cell, quickly followed by two or three others, is differentiated 
in the xylem rod. In the majority of the plants examined this parenchyma 
strand occupied a markedly excentric position, the appearance presented by 
this isolated section reminding one of the normal structure of Lindsay a. 
The excentric position in Dicksonia , however, is evidently merely connected 
with the exit of the first leaf-trace, which is concentric in structure, and 
formed in a perfectly simple manner. It will be noticed that no sieve- 
tubes appear in the central parenchyma before the exit of the first trace, 
a state of affairs differing from that obtaining in Alsophila. In one case, 
however, a well-marked sieve-tube was observed in the parenchyma 
between the cauline strand and the outgoing leaf-trace, and this point, 
in conjunction with the fact that only four specimens of this fern were 
available for examination, would seem to indicate that, in all probability, 
internal phloem is differentiated before the first leaf-trace, just as described 
for Alsophila. 
At the exit of the trace, phloem appears on the inner surface of the 
vascular arc, and, after the closing of the gap, we have a ring of xylem 
enclosing a strand of phloem, largely parenchymatous, and surrounded by 
a phloem sheath in which the narrow deeply-staining sieve-tubes are very 
conspicuous. At this level a considerable amount of parenchyma occurs in 
the xylem, often so arranged as to break the xylem ring into two or three 
arcs. The ring-like character of the vascular tissue as a whole, however, is 
perfectly obvious. 
The vascular ring then becomes strongly elliptical in outline, receiving 
a root-trace at one end of the ellipse. The next leaf-trace is formed 
exactly opposite the root, its gap closing somewhat abruptly. During 
1 Observations on the anatomy of Solenostelic Ferns, II. Annals of Botany, xvii. 
