ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 945 
The phenomena of secondary growth, remarkable as they are, have appeared in so 
many diverse groups of Cryptogams and Phanerogams, that we cannot attach much 
systematic importance to them. 
The special peculiarities of the secondary tissues in Sphenophyllum appear to us to 
have been somewhat exaggerated by previous authors. For example the absence of 
medullary rays, on which so much stress has been laid, does not seem to have been 
constant in any species, while in S. insigne, which we have proved to be a true 
Sphenophyllum, such rays are present in all parts of the wood. The structure of 
the secondary tracheze does not seem to us to differ essentially from that in other 
Cryptogams with indefinite growth in thickness. Their structure has been misunder- 
stood in the past, and represented as much more peculiar than it really is. The 
question whether these elements are vessels or tracheides must, indeed, be left open. 
Even if they are true vessels they are not without analogy among recent Cryptogams. 
Prof. Harvey Gipson has been good enough to inform us that in Selaginella 
rupestris and oregana, he finds perfectly typical vessels, with transverse septa which 
become completely perforated, only leaving an annulus to mark their position.* 
The cambium of Sphenophyllum is perfectly normal, we might almost say typical. 
The most remarkable point is the repeated formation of internal layers of periderm. 
This has no exact parallel in other Cryptogams, though familiar enough among higher 
plants. 
The root-like anatomy of the stem is highly characteristic, and indeed peculiar to the 
genus. The nearest approach to it is to be found in the centripetal xylem-strands of 
such Lycopods as Psilotum or Tmesipteris, with which, however, our plant has 
otherwise nothing in common.t 
In conclusion, we must return for a moment to the fructification, in order to 
explain more clearly M. ZeruuEr’s views of its relation to that of Marsilia and of 
Ophioglossum. This author (loc. cit., p. 37) points out the similarity between the 
pedicel of the sporangium in Sphenophyllum, and the stalk of the sporocarp in 
Marsilia. In both, the position is that of a ventral lobe of the leaf, while the mode 
of attachment of the sporangium in the former is similar to that of the sporocarp in 
the latter. We cannot, for our part, see more than a superficial resemblance here, 
for it seems to us impossible to compare morphologically the single sporangium of a 
* Prof. Grson will give details in his forthcoming paper on the “ Comparative Anatomy of Selaginella.” 
[This has since appeared in the ‘ Annals of Botany,’ vol. 8, number for June, 1894. July 15, 1894] 
+ We cannot follow Count Sorms-LavBacn in his remarks on this subject. He says (oc. cit., p. 354) : 
“ Assuming that the primary central bundle [in Sphenophyllum] belongs to the concentric type, then it 
may no doubt be compared with the axile strand of Lycopodiee. But this is as yet only an assumption ; 
the bundle might just as well be a triarch radial strand, and then there would be no resemblance to the 
structure of the stalk in any known living plant.” We have little doubt that the central strand in 
Sphenophyllum is radial, in pp Bary’s sense, and that it is either triarch or hexarch. But surely the 
central strands of existing Lycopods are radial also, as DE Bary long ago showed, and as the development 
clearly proves, 
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