Danaea and other Marattiaceae. 523 
Haplostele. A simple type of stele, frequently found in 
seedling Pteridophyta, rhizome of Hymenophyllaceae, &c. It 
consists of an axial rod of tracheae surrounded by a ring of 
phloem. The ‘ pericycle ’ is included if differentiated from the 
procambium-strand. If central parenchyma is present, then 
to be described as a medullated haplostele. 
‘ Solenostele.’ A continuous amphiphloic tube of vascular 
tissue with widely separated leaf-gaps. Pericycle present and 
the tube delimited by an external and internal endodermis. 
Dictyostele. A vascular tube with large ‘ overlapping ’ 
leaf-gaps, so that the whole structure becomes a network of 
vascular strands or meristeles. The meristeles are concentric. 
This is closely allied to the preceding, the difference being 
due to the approximation and overlapping of the leaf-gaps. 
The dictyostele is further defined as siphonic when the net- 
work is simple and tubular, adelosiphonic when complex, 
i. e. ceasing to be obviously tubular. 
c Protostele.’ A stele which is supposed to be primitive in 
structure. Has been applied to both haplo- and actinostelic 
types. 
Hysterostele. A stele which is supposed to be reduced in 
structure, e. g. in Hippuris , Potamogeton and Hottonia (aquatic 
stem). 
Meristele. The vascular bundle in the old sense, except 
that it does not include actino- and haplosteles as formerly. 
It therefore applies to the vascular bundles of the stem of 
Dicotyledons and Monocotyledons, the ‘concentric vascular 
bundles ’ of Pteridophyta, and vascular bundles of outgoing 
leaf-traces and leaves. 
Development of the Vascular System of 
Danaea simplicifolia. 
A number of seedling plants of various ages were available, 
and these were examined chiefly by means of microtome 
serial sections. The sections were usually doubly stained 
with haematoxylin and safranine and mounted in Canada 
balsam. The advantage of this method of staining, when 
