Zs 
ganisms may have obtained their energy for building up organic 
from inorganic materials 
— 
, much as certain modern bacteria do, by 
the oxidation of carbon, nitrogen, sulphur, or iron by what is called 
chemosynthesis, and that what might be called the first stage of 
evolution preceded the evolution of chlorophyll or “ leaf green,” 
the possession of which distinguishes plants from animals and en- 
ables the former to utilize the energy of the sun, by photosynthesis, 
to obtain carbon from the carbon dioxide of the air, and build com- 
plex organic starches and sugars from inorganic materials. 
Once chlorophyll was evolved we would have plants much like 
the Cyanophyceae or blue-green algae, which would serve as a start- 
ing point for the more complex green 
fants. Meanwhile the evo- 
lution of metatrophic bacteria, which derive their carbon from 
— 
other organisms, would forever prevent any subsequent origin of 
life, and effectually answer the question so often raised: “If the 
organic originated from the inorganic onee why can it not do so 
repeatedly ?’ 
The evolutionary history of plants may be divided, then, into a 
first and hypothetical pre-chlorophyllic or ophytic stage, and a 
second and entirely objective chlorophyllic stage. The latter 
would, at first, constitute what might be called an algae substage, 
since it 1s clear from all lines of evidence, as well as from what we 
know of geological history, that all land plants were derived from 
algal ancestors. 
2. Algae 
The mutual relations among the various classes of algae are much 
too abstruse to be set forth in this connection, but we can visualize 
a progression from unicellular to multicellular and from planktonic 
(floating) to benthonic (deep-water or bottom) habits. 
The nature of the algal plant body, without a cuticularized epi- 
dermis (cutin) and without mechanical tissue (lignin), results in 
the total oxidation of algae before they can be covered by sedi- 
ments and preserved as fossils; or, if they happen to be so pre- 
served, the fossil 1s a mostly undecipherable impression from which 
little of its true nature can be obtained. This is true of all algae 
except those whose life processes cause the deposition or secretion 
of calcareous material. Indefinite impressions of non-caleareous 
algae have been recorded from pre-Cambrian times through all 
