254 SCIENCE PROGRESS. 



lished his memoir " On the Structure and Affinities of the 

 Plants hitherto known as Sternbergiae" (21). These curious 

 fossils, in their typical form, are cylindrical bodies, marked 

 with constrictions at very short intervals, so that the whole 

 has been compared to a pile of coins. Williamson was the 

 first to prove that these StembergicB, or Artisics as they 

 were also named, represent casts of the medullary cavity of 

 a Dadoxylon, the constrictions marking- the position of the 

 diaphragms by which the fistular pith had been chambered. 

 The paper is an admirable one, and the anatomical details of 

 the tissues of the stem were worked out with great accuracy 

 for that period. We now know that Dadoxylon was the 

 stem of Cordaites, so we see that Williamson, in this early- 

 paper, made one of the first contributions towards building 

 up the very complete knowledge which we now possess of 

 this remarkable extinct family of Gymnosperms. 



The characteristic work of Williamson, on which his 

 reputation as a leader in Fossil Botany will rest, was that 

 on the microscopic structure of Carboniferous plants. The 

 paramount importance of such studies is, perhaps, hardly 

 appreciated by systematic botanists, who, in dealing with 

 recent plants, are accustomed to rely almost entirely on the 

 more external morphology, and particularly on that of the 

 reproductive organs. Evidence of this kind, however, is 

 often wanting in the case of fossil plants, and when we are 

 dealing with families so far back in the past, and so remote 

 from any now living, as those of the Carboniferous Flora, it 

 is obvious that the mere external characters of vegetative 

 organs must be a very insufficient guide. Indeed even where 

 the reproductive organs are preserved, little can be made of 

 them, at any rate if they are Cryptogamic, without reference 

 to their minute structure. Consequently it is hardly too 

 much to say that, as regards the earlier formations, no 

 knowledge of the Flora, which is of botanical value, can be 

 acquired without the aid of histological characters, in addi- 

 tion to those of a more obvious kind. 



So far as the Carboniferous strata are concerned there is 

 happily no lack of magnificently preserved material for 

 structural investigation, and it was by the thorough study 



