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10 THE BRITISH FERNS. 
tree Ferns, a few bundles larger than the rest, are closely surrounded 
with dense tissue, and disposed symmetrically around the axis, 
sometimes forming a close cylinder, as in Dicksonia antarctica. Mr. 
Berkeley mentions* a tree Fern from Sylhet, in which this cylinder 
was found to be nearly perfect. In some cases, Mr. Berkeley con- 
tinues, they seem to be quite isolated, giving off no bundles to the 
fronds, this office being performed by smaller fascicles, as in the tree 
Ferns figured by Mohl;t while in others, they as evidently supply 
the stipites. 
The general disposition of the tissues in the more highly organ- 
ised forms of Ferns, has been described as follows : |—Round the 
scars of the stipites there are cavities filled with stellate brown 
tissue. The cortical stratum consists first of cuticle, then of paren- 
chym, and then a harder layer of brown sometimes parenchymatous 
sometimes prosenchymatous tissue with thick punctated walls. The 
enclosed cylinder is filled with softer cellular tissue, containing 
many cysts gorged with resinous matter, and various bundles 
of vascular tissue, attended by pale pleurenchym. The larger 
bundles which are flattened and variously curved, are surrounded 
by dense tissue like the inner layer of the bark, and arranged in a 
circle symmetrically round the axis, with short interspaces, through 
which the other smaller bundles dispersed in the central mass 
give off branches into the stipites, while others exist in the space 
between the bark and larger masses. . These latter form a cylinder, 
more or less perfect, round the axis, and are altogether distinct from 
anything in endogenous stems, besides which there is not that 
crossing of the fascicles characteristic of Endogens. The vessels 
Mr. Berkeley states are always scalariform; but Dr. Lawson 
informs us, that he has frequently found unrolled spiral vessels. 
* Berkeley, Introduction to Cryptogamic Botany, 514 (note). 
+ Martius, Zcones Selecta Plantarum Cryptogamicarum Brasiliensium, tt. 29-36. 
X Berkeley, Introduction to Cryptogamic Botany, 514. 



