222 EVOLUTION OF PLANTS 



lime and seem to have played an important r61e in rock- 

 building. That anomalous group, the Characese, is also 

 represented in the later formations by a considerable 

 number of unmistakable forms. These too, owe their 

 preservation to the calcareous deposit in their cell-walls. 

 The Characese are represented not only by fragments of 

 stems, but also by the curious spore-fruits, which are 

 exactly like those of the living types. The earliest of 

 these Characese occur in the Miocene rocks. Certain 

 red algse, Corallinese, are abundant in the Mesozoic 

 rocks, and probably occurred in the later Palseozoic for- 

 mations. Many of these are referable to existing genera, 

 and closely resemble forms which are still living. 1 



Among the Algse, one group, the Diatoms, have left 

 very abundant remains, but as yet these have been found 

 only in the more recent strata. As the silicious shells 

 of these plants are very permanent, their complete absence 

 from Palseozoic rocks seems to indicate that the group is, 

 comparatively speaking, a recent one. The deposits of 

 diatoms are extraordinarily abundant in the later for- 

 mations, the first ones occurring in the Mesozoic rocks, 

 where, however, they are much less abundant than in the 

 Tertiary formations. The flinty valves or shells are 

 perfectly preserved, and make their identification an 

 easy matter. Many of the genera and even species are 

 identical with living ones. The diatomaceous deposits 

 are often of astonishing thickness, showing that these 

 plants, as at present, occurred in enormous masses 

 together. 



The fossil fungi are too few and imperfect to 



1 The most recent investigations point to the existence of Coralline 

 algse and Siphonese in the early Silurian deposits. 



