CHAPTER XII 



GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION 



The history of the Plant Kingdom as revealed by the 

 geological record is necessarily very fragmentary, but 

 nevertheless the study of fossil plant remains has yielded 

 most important evidence for tracing the succession of 

 plant forms. The record is most unsatisfactory with 

 reference to the lower plants, whose delicate tissues are 

 poorly fitted to leave recognizable remains in the rocks. 

 Long before there is any absolute evidence of the ex- 

 istence of plants, it must be assumed that these lower 

 plants were present upon the earth, but naturally their 

 delicate and extremely perishable structures have left no 

 fossil traces. Indeed, throughout the Thallophytes, with 

 few exceptions, the fossil remains are so imperfect that 

 a satisfactory estimate of their real nature is often quite 

 impossible. 



The ferns and their allies have been preserved in many 

 cases with remarkable perfection, and the same is true 

 of many flowering plants, especially in the later forma- 

 tions, and among the AlgEe a few groups possessing 

 silicious or calcareous cell-walls, have been preserved 

 in a recognizable form, but these nearly all belong to 

 the later formations and throw no light upon the char- 

 acter of the earliest forms. Among the vascular plants, 

 however, the tissues are sometimes preserved with such 



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