Ceratopteris thalicir aides, (L.) 1 1 3 
Comparing the above results with those given by Leclerc du 
Sablon 1 in the case of Pteris aquilina , Trie Romanes alatum , 
Osmunda regalis and Angiopteris evecta, we find that Cerato- 
pteris agrees with the above Ferns as far as that stage in 
development which is represented by Fig. 5. No resem- 
blances are found beyond this point, for in Ceratopteris the 
solid stele divides directly into two, whilst in the Ferns 
described by Leclerc du Sablon a ring of xylem is formed by 
the appearance of pith or phloem in the centre of the solid 
xylem-strand. No such ring can be detected in Ceratopteris, 
for the xylem is always present as a solid central mass, and 
the parenchymatous cells which may or may not be scattered 
irregularly amongst the tracheids can hardly be regarded in 
the light of phloem or medullary tissue. 
Van Tieghem 2 has described polystely as a modification of 
the original pithless monostele, which by repeated bifurcations 
gives rise to several steles. Jeffrey 3 , in his work on the 
morphology of the central cylinder of Angiosperms, states 
that polystely does not arise in this way. According to this 
author, the primitive condition is represented by the type 
found in the young stages of all polystelic Ferns and Angio- 
sperms examined by him, viz. a tubular stele with an inner 
and an outer endodermis. In no case has he found this 
bifurcation of a pithless monostele described by Van Tieghem. 
In Ceratopteris , however, Van Tieghem’s description of poly- 
stely seems to hold good, for no trace of a tubular stele is 
found. 
A certain amount of consideration must, however, be given 
to the fact that Ceratopteris occupies a somewhat isolated 
position amongst the Filicineae owing to its aquatic or semi- 
aquatic manner of life. The reduction of the stem, the 
absence of sclerenchyma, and, above all, the small size of the 
individual vascular elements, can all be traced to this cause, 
and it seems possible that this comparatively simple type of 
arrangement in the development of the polystelic stem may 
1 Leclerc du Sablon, 1890, p. 5. 2 Van Tieghem, 1886, p. 282. 
3 Jeffrey, 1899, p. 613. 
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