STRUCTURE OF FOSSIL PLANTS 73 



secondary wood on both sides of it, and within these a 

 number of small steles, all scattered through the ground 

 tissue, and each surrounded by secondary wood. In 

 actual specimens the number of these central steles is 

 much greater than that indicated in the diagram. 



No plant exists to-day which has such an arrangement 

 of its vascular cylinder. It almost appears as though at 

 the early period, when the Medulloseae flourished, steles 

 were experimenting in various directions. Such types 

 as are illustrated in figs. 50 

 and 51 are obviously waste- 

 ful (for secondary wood de- 

 veloping towards the centre 

 of a stem is bound to finally 

 meet), and complex, but 

 apparently inefficient, which 

 may partly account for the 

 fact that this type of struc- 

 ture has not survived to the 

 present, though simpler and 

 equally ancient types have 

 done so. 



Further details of the 

 anatomy of fossils will be 

 mentioned when we come to consider the individual 

 families; those now illustrated suffice to show that in 

 the Coal Measures very different arrangements of steles 

 were to be found, as well as those which were similar 

 to those existing now. The significance of these differ- 

 ences will become apparent when their relation to the 

 other characters of the plants is considered. 



The fructifications, always the most important parts 

 of the plant, offer a wide field, and the divergence be- 

 tween the commoner palaeozoic and recent types seems 

 at first to be very great. Indeed, when palaeozoic repro- 

 ductive bodies have to be described, it is often necessary 

 to use the common descriptive terms in an altered and 



wider sense. 



( 122 ) 7 



Fig. 51. — Continental Medullosa, show- 

 ing R, outer double-ring stele with second- 

 ary wood all round it ; s, inner stellate 

 steles, also surrounded in each case by 

 secondary tissue 



