GEOGRAPHICAL DISTRIBUTION 



169 



remains (relict endemics) of a genus of several specie^, 

 which, in Tertiary times, was widespread over most of 

 the northern hemisphere (Fig. 77). 



By a like balancing of evidence we are able to ascertain 

 that the ubiquitous fern family, Polypodiacea, with 

 some 200 genera and about 3,000 species, is a com- 

 paratively modern group, while the Osmunda family, 



FIG. 77. Map showing the known geographical distribution of Se- 

 quoia during the Cenozoic era. The cross indicates the only known loca- 

 tion of living specimens. (After E. W. Berry.) 



with only two (or possibly three) living genera and some 

 ten species, and with wide but discontinuous distribution, 

 is much older. The greater antiquity indicated for the 

 Osmundaceae by the facts of their geographical distribu- 

 tion is also attested by fossil evidence, and further by the 

 nature of their spores. The spores when mature contain 

 chlorophyll, and this fact, of itself, indicates antiquity; 

 for this and other structural and physiological reasons, 



