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 Thallopbytes, 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 Alge 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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