222, EVOLUTION OF PLANTS 
lime and seem to have played an important réle in rock- 
building. That anomalous group, the Characez, 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 Characez 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 Characeze occur in the Miocene rocks. Certain 
red alge, Corallinee, are abundant in the Mesozoic 
rocks, and probably occurred in the later Paleozoic for- 
mations. Many of these are referable to existing genera, 
and closely resemble forms which are still living.t 
Among the Algz, 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 Palzozoic 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 
algee and Siphonez in the early Silurian deposits. 
