CONCLUSION 233 



fore safely conclude that during all such periods 

 adaptation to the existing circumstances has been 

 for practical purposes complete. If the plants of 

 later periods seem to us more perfect than their 

 predecessors, it is because they are adapted to 

 conditions with which we are more familiar, and 

 which are also, in some respects, more complex. 

 However far back we may follow the fossil records, 

 we shall never meet with badly-adapted plants 

 only with plants adapted to different conditions 

 from those of the present. Certain conditions 

 have remained constant all through, and where 

 this is the case, we find just the same constructions 

 in Palaeozoic as in recent plants. 



The long, rather narrow leaves of the Cor- 

 daitese were fitted to resist mechanical strains 

 in the same way as Monocotyledonous leaves of 

 similar shape at the present day. In both 

 there are parallel ribs of strong fibrous tissue 

 running through the leaf near the upper and 

 lower surface, i. e. in the position where they 

 afford the most resistance to bending with the 

 least expenditure of material. In the outer 

 cortex of the stem of Lyginodendron and many 

 other Palaeozoic plants, there are bands of fibres 

 united to form a network, the meshes of which are 

 filled up with the softer cellular tissue. This 

 formed an admirable means of support, placed 

 at the outside of the cylindrical stem, where it 



