may 1899] ON THE ANATOMY OF FOSSIL PLANTS 



3°5 



characteristic appearance in some of the casts ; but, inasmuch as later 

 research has shown that the same structure is common in the outer 

 cortex of many quite distinct Palaeozoic plants, the name Lyginodcndron 

 lost its generic significance until Williamson adopted it for some 

 specimens showing internal structure, which he believed to be identical 

 with some of the casts to which the name had been originally applied. 



Unfortunately, as already mentioned, nothing whatever is known 

 as to the organs of fructification of any of these forms, or, at least, if 

 they are known they have never been correlated with the vegetative 

 organs. " So long as the mode of reproduction is unknown, it will be 

 impossible to assign these genera definitely to their systematic position ; 

 in the meantime, we can only weigh with due care such evidence as is 

 afforded by their vegetative structure. This evidence, as we shall 

 show, clearly indicates, as far as it goes, a position intermediate 

 between ferns and cycads." 1 



However, the taxonomic value of anatomical characters is gradually 

 becoming more and more recognised. Dr. Scott, in his Presidential 

 Address to the Botanical Section of the British Association in 1896, 

 referring to this, instances the Marattiaceae as an example, pointing 

 out that in this old fern-family there is great uniformity in anatomical 

 structure, while the sporangia show the important differences on which 

 the distinction into genera is based. 



Another good example may be found in the Calamites, the 

 structure of which has been worked out with very great completeness 

 by Williamson ; and later, by Williamson and Scott. 2 These later 

 researches have shown that the primary structure of these common 

 Coal Measure fossils, is essentially so exactly that of an Eavisetum, as 

 to leave no question as to their near relationship, and they have 

 accordingly been placed in the Equisetales. And yet, so recently as 

 the publication of Solms-Laubach's " Fossil Botany" in 1887, we find 

 the Calamites treated of in quite a distinct part of the book from the 

 Equisetaceae, recent and fossil. A most interesting historical sketch of 

 the growth of opinion as to the affinities of the Calamites will be found 

 in the recently published valuable introduction to the botanical study 

 of fossil plants by Mr. A. C. Seward. 3 



Returning to the Lyginodendreae, in Lyginodendron the stele of the 

 stem consists of a central pith, around the periphery of wdiich are a 

 number of distinct strands of primary xylem, external to which is seen, 

 in most cases, a broad zone of secondary wood, the elements of which 

 are arranged with great regularity in radial rows. The primary bundles 

 are distinctly collateral in structure and exhibit a distribution of 

 their elements, which is of the highest importance for comparison with 



1 Loc. tit. p. 704. 



2 "Further Observations, etc. Parti. Calamites, Calaniostaehys, and Sphenophyllum." 

 Phil. Trans. (1894), vol. clxxxv. p. 863. 



3 "Fossil Plants," Cambridge University Press, 1898, vol. i. pp. 295-302. 



