STRUCTURE OF FOSSIL PLANTS 59 



From the morphological standpoint, also, the features 

 of the plant body from the Coal Measure period fall into 

 the same divisions as those of the present. Roots, stems, ^ 

 leaves, and reproductive organs, the essentially distinct I 

 parts of a plant, are to be found in a form entirely recog- 

 nizable, or sufficiently like that now in vogue to be 

 interpreted without great difficulty. In the detailed 

 structure of the. reproductive organs more changes have 



Fig. 34. From a Photo of a Fossil Leaf 



c, Epidermis; p, palisade cells; pr, soft parenchyma cells (poorly preserved); 

 s, sclerenchyma above the vascular bundle. 



taken place than in any others, both in internal organiza- 

 tion and external appearance. 



Already, in the Early Palaeozoic period, the distinction 

 between leaves, stems, roots, and reproductive organs 

 was as clearly marked as it is to-day, and, judging by 

 their structure, they must each have performed the physio- 

 logical functions they now do. Roots have changed least ,/ 

 in the course of time, probably because, in the earth, they 

 live under comparatively uniform conditions in whatever 

 period of the world's history they are growing. Natu- 

 rally, between the roots of different species there are 

 slight differences; but the likeness between fern roots 

 from the Palaeozoic and from a living fern is absolutely 

 complete. This is illustrated in fig. 35, which shows the 



