PART III. 



I. Introductouy Remarks. 



In the Part last piiblislied of this Monograph a deviation was made from the plan 

 first proposed, in considering some of the Organs of Fructification of Fossil Plants, and 

 leaving the treatment of the structure of the Stems for a time. I will now, therefore, 

 return to the original intention of describing the internal structure of several specimens of 

 Fossil Woods from my own cabinet and that of Mr. J. S. Dawes. These are in a good 

 state of preservation, and will afford some additional information on the genus 

 Lepidodendron. 



After the investigations of AVitham, Lindley and Hutton, Brongniart, Hooker, and 

 others, nearly every portion of the structure of the stem had been made out, with the 

 exception of the medulla. It was more inferred than proved that the structure of this 

 part consisted of cellular tissue in the Rev. C. G. W. Harcourt's specimen found at 

 Hesley Heath. Mr. Dawes' specimen, however, figured in Plate VII, and described in 

 Part II of this Monograph, clearly proves that the above-named authors were in the 

 main right in stating that the medulla of Lepidodendron was composed of a cellular tissue 

 which was not ordinary parenchyma, like such as is found immediately outside the vas- 

 cular cylinder ; for it consisted of large rectilinear cells, arranged in vertical series, some- 

 thing like bricks upon their ends, as first noticed by Mr. Dawes to occur in Ilalonia. 

 This beautiful Lepidodendron, probably the most perfect in its state of preservation of any 

 with which we are acquainted, will be described in detail before I proceed to consider 

 the genus Halonia, and to show the relation of that fossil to Lepidodendron. Some 

 remarkable instances of the division of the vascular axes of Lepidodendron, Ilalonia, and 

 Sigillaria vascidaris, just before the stems of those plants dichotomize, will be given. 

 These fully confirm Brongniart's views, as stated in his admirable memoir on Les 

 Lycopodiacees, in the second volume of his ' Histoire des Vegetaux fossiles.' 



I shall then restate the chief part of what has been published on the structure of 

 Ilalonia. Next a description of Mr. Dawes' and my own specimens will be given in 

 detail. In conclusion, it is intended to show the connection of Ilalonia with Lepidoden- 

 dron, so far as their structure is concerned. 



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