Danaea and other Marattiaceae. 
52i 
which all are familiar. The word would apply whether the 
dictyostele were tubular as a whole (Bundel-Rohr of De Bary), 
as in Aspidium , or consisted of an irregular compound network 
of anastomozing strands as in P ter is aquilina and Angiopteris 
evecta. Jeffrey 1 has proposed the term adelosiphonic to 
describe the * siphonostelic central cylinder ’ when it ‘ ceases 
to be obviously tubular.’ Adopting his terms, the clearly 
tubular dictyostele would then be described as siphonic and the 
more irregularly constructed form as adelosiphonic. 
In certain cases the central cylinder seems to be clearly 
reduced, or modified, as a result of habitat, e. g. in Hottonia , 
aquatic stem, and in Potamogetons , &c. The term hysterostele 
would distinguish these forms satisfactorily. Having thus 
named and described the chief types of stele, the question 
remains to be considered how to speak of the individual 
strands of any of those steles. The term meristele would 
seem to answer, but modified from its original meaning as 
used by Van Tieghem and Strasburger. A sense in which 
it has been used and in which it is proposed to be used here 
is due to Jeffrey, who applies the word to the individual 
strands of any vascular system. The application of the term 
will not be confined to the vascular strands of the stele only, 
but will be extended to those of the outgoing leaf-traces and 
their continuation into the leaves. This is done purely as 
a matter of convenience, on account of the apparent identity 
in structure, in most cases, of those strands, not on account 
of any theoretical considerations as to how the leaf bundles 
become continuous with those of the stem or vice versa. The 
terms collateral, bicollateral and concentric, can be just as 
well applied to the same types as under the old vascular 
bundle terminology, with this gain that haplosteles and 
actinosteles are not included. The f steles,’ or now meri- 
steles, of some of the ‘ polystelic ’ Primulas and Gunner as 
are reduced eusteles in structure, and if desired could be 
simply described as eumeristelic , and those of the simple fern- 
1 E. C. Jeffrey, The Structure and Development of the Stem in the Pteridophyta 
and Gymnosperms, Phil. Trans. Royal Society, vol. cxcv, 1902, p. 144. 
