Anatomy of Solenostelic Ferns . 701 
often they form long splits interrupted by small meristeles 
passing across the lacuna from one side to the other. 
Although a completely closed vascular ring is sometimes 
to be met with in transverse sections of the internode, the 
most frequent appearance is that of two large curved meri- 
steles, one dorsal and one ventral, with or without one or 
two smaller ones lying between their margins. In this plant, 
therefore, an entirely exceptional kind of dictyostely has been 
attained without relation to the overlapping of the leaf-gaps ; 
indeed so far as that is concerned the vascular structure may 
still be regarded as solenostelic. So far as I am aware, in 
this respect Dicksonia rubiginosa stands unique among the 
Ferns. 
The accessory vascular strands found within the ordinary 
stelar cylinder vary in number from point to point. There 
were never more than three present in my specimen, and 
sometimes they all fused up to a single large curved strand. 
In their course through the internode they may branch and 
anastomose with each other, but they never come into contact 
with the internal surface of the ordinary stelar cylinder except 
in the neighbourhood of the nodes. At each node a single 
internal strand approaches the free margin of the leaf-gap, and 
gradually fuses with it until the two xylems are perfectly con- 
tinuous, presenting an appearance exactly as in Dicksonia 
adiantoides . As soon as the leaf-trace has departed it separ- 
ates off again and passes on as a free internal strand into the 
internode above. One internal strand at least was present in 
all parts of the specimen examined, even at the base of the 
narrow lateral shoots. Distinct mesarch protoxylem groups 
are to be found in them, which, however, do not appear to be 
in any way related to those of the leaf-trace. In this plant, 
again, the vascular systems of lateral shoots are usually to be 
found departing from the margins of the petiolar strand, 
and, as in Dicksonia adiantoides , small vascular strands are 
sometimes to be met with which run forward from the internal 
surface of the leaf-trace to the free margin of the leaf-gap. 
A still more conspicuous system of internal vascular strands 
