690 G wynne- Vaughan . — Observations on the 
the original central stele has in this manner become broken 
up will be called ‘ meristeles.’ 
The most primitive type of vascular system that occurs in 
the Filicineae is probably the single protostelic central cylinder 
of the mature stem of Lygodium , the most important char- 
acteristic of which is that the continuity of the central 
xylem mass is not interrupted by the subsidence of the 
external tissues, cortical or vascular, at the departure of 
the leaf-traces. Such a structure has not yet been found in 
the mature stem of any of the Cyatheaceae or Polypodiaceae, 
although it is sometimes to be met with at the very base 
of the young plant. The solenostele holds an intermediate 
position between this simple protostelic type and the more 
complicated dictyostelic arrangements most frequently ex- 
hibited by these two orders, and it is chiefly due to this 
fact that the solenostele becomes a structure of particular 
interest. 
The earliest reference to the solenostelic type of structure 
was made in 1838 by Robert Brown 1 , who noted the presence 
of a complete ring of vasa scalariformia in Polypodium Hors- 
jieldii , R. Br. ( Dipteris conjugata , Reinw.). A similar structure 
has since been recorded by various botanists in a large number 
of different Ferns, although many of their so-called ‘pith- 
containing wood-cylinders ’ have proved upon investigation to 
be really dictyosteles and not solenosteles. Most of the 
examples included in this paper have already been mentioned 
at one time or another, and although most of the previous 
descriptions have been more or less inadequate or incorrect, 
those given by Karsten 2 and Mettenius 3 can hardly be 
improved upon. The true solenostele is not of very general 
occurrence, although it is to be met with in several different 
genera, e. g. Dicksonia , Davallia , Lindsay a, Hypolepis , P ter is, 
1 Horsfield, Plantae Javanicae, p. 2. 
2 Die Vegetationsorgane der Palmen. Abhandl. d. K. Acad. d. Wissensch. 
z. Berlin, p. 186, 1847. 
3 tjber den Bau von Angiopteris. Abhandl. d. K. Sachs. Gesellsch. d. Wissen- 
sch., Bd. vi, p. 531, 1864. 
