[Kirsch] CERTAIN STRUCTURES IN THE PTERIDOPHYTES 385 
groups of cells are identical with the above mentioned Liickenparen- 
chymzellem, but Russow does not appear to have seen this connection. 
The next mention of these structures is by De Bary. Speaking of 
the ferns in general, he says (8, 346): “ In petioles, when the xylem is 
concave or notched, strands of cells three to four rows thick, which are 
distinguished from the rest of the parenchyma by their very wide lumen, 
are to be found in its depressions and furrows, sometimes just in front 
of the primitive tracheides.” He then proceeds to give Russow’s ob- 
servations on the Polypodiaceæ. As examples of the forms in which 
these structures are found he mentions species of Asplenium, Cyathea 
microlepis, Asplenium filix-fœmina, and Cyathea medullaris. 
In describing the bundie in tne petioie of Osmunda, he says 
(3, 347) : “On the concave side it is parenchymatous, and distinguished 
in cross section by ten to twelve small groups of conspicuously wide 
cells, which still need investigation.” That he connected these with the 
“ Lückenparenchym ” of Russow is evident from what he says at the 
end of the passage quoted above (8, 346), which runs as follows: “ The 
wide cells in Osmunda regalis to be mentioned below may also belong 
here.” De Bary did not make any attempt to interpret these structures 
and merely stated what he and others had observed. 
Thus far, only the structures which will be shown to be thyloses 
blocking up a canal have been discussed, no mention being made of the 
canal itself. However, De Bary also refers indirectly to the canal, or to 
be more exact, ‘to similar canals in other forms than those under dis- 
cussion. 
In the section treating of the structures of the vascular bundle, the 
following is significant in view of what will be shown below (3, 318). 
“The elements of the vascular bundle are, as far as investigations reach, 
almost everywhere and always in uninterrupted connexion, both among 
themselves and with those of the surrounding sheaths. The only not 
uncommon exceptions are that the xylem, especially in collateral bundles, 
shows intercellular spaces containing air at its inner edge, and that 
spaces containing secretions lie in the outer regions of the bundle.” 
“ Collateral bundles are with rare exceptions characteristic of the 
stem and foliage leaves of the Phanerogams, also of the stem of Equi- 
seta, Ophioglosseæ, Osmunda, and Todea (?).” 
That De Bary did not observe any canals in the vascular bundles 
of the Pteridophyta (except in Equiseta) is evident from what he says 
further on (3, 326). 
“Tn the xylem of many collateral bundles an intercellular passage 
occurs, which follows the course of the whole bundle, sometimes next 
