Some Recent Work on the Anatomy of 



Fossil Plants. 



By Arthuk J. Maslen, F.L.S. 



No plant types are more interesting, and certainly none have yielded 

 more valuable results to the palaeo-botanist during the last few years, 

 than the numerous forms now known which present intermediate 

 characters tending to unite the ferns with the cycads. 



These synthetic forms (of which, unfortunately, the reproductive 

 organs are in no case known), have recently been made into a group — 

 the Cycadofllices, and this again may be conveniently divided into two 

 fairly distinct series ; the first including such types as Lyginodendron, 

 Heterangium, Poroxylon and Protopitys, in all of which the stem is 

 essentially monostelic (containing only a single vascular axis) ; and 

 the second containing a series of forms, the stems of which exhibit a 

 more or less complicated polystelic structure, well seen in the most 

 familiar forms — the Medulloseae. 



The two most interesting monostelic forms, Lyginodendron and 

 Heterangium, are common in the calcareous nodules of the English 

 Coal Measures, and have formed the subject of the last of the valuable 

 contributions to palaeontology made jointly by the late Professor W. 

 C. Williamson and Dr. I). H. Scott. 1 The material with which these 

 two botanists were able to work was so good, and the preservation of 

 the vegetative organs so perfect, that it was possible to work out the 

 structure in great detail, and to arrive at such certain conclusions as 

 would astonish the botanist unacquainted with modern palaeo-botanical 

 research. To such the illustrations in this memoir (and in others) 

 will be a revelation. 



The generic name, Lyginodendron, was originally applied by Gourlie 

 to casts of stems exhibiting what is now generally known as the 

 " dictyoxylon structure." This structure, which consists of the presence 

 in the outer cortex of a strengthening tissue, composed of an anastomos- 

 ing longitudinal network of sclerenchymatous strands, leads to a very 



1 "Further Observations on the Organization of the Fossil Plants of the Coal-Measures. 

 Part III. Lyginodendron and Heterangium," Phil. Trans. (1895), vol. clxxxvi. B. pp. 703- 

 779, pis. 18-29. 



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