300 
The Ohio Naturalist. 
[Vol. V, No. 5, 
dryland plants the water taken from the soil into the bodv of the 
plant is sufficient for carrying on all the essential processes of life. 
From certain morphological characteristics the three great 
groups or series have been called Thallophyta, Archegoxiata, 
and Spermatophvta, or in English, Thallophytes, Archegoniates, 
and Spermatophytes or Seed Plants. It must not l.)e supposed, 
however, that all plants live in the habitat to which thev seem to 
have been adapted originally. The great maiority of Thallo- 
phytes now live in the air, many Archegoniates are found in verv 
dry places, while great numbers of Seed Plants have returned to 
the water. 
The general progress of the history of the earth’s surface has 
been from an aqueous condition to a dry land condition. Plants 
originated in the water and since islands and continents arose 
from the primordial ocean they have been stranded on the shores 
and crowded from water to aerial conditions by the drying of 
swamps and seas. When drier conditions began to prevail on 
the enlarging islands and continents, the lack of free water was 
met by the development of seeds. The progressive advance- 
ment of the general mass of the plant kingdom has plainly been 
along the lines of the earth’s ])hysiographic history. It must not 
be concluded however, that the evolution of plants was entirely 
or even to a considerable extent due to environment but onlv 
that the evolutionary process has kept pace with jihysiographic 
changes on the earth. The evolutionary processes are primarily 
the result of protoplasmic properties and functions. Organisms 
in the past were as well adajAed to live in their environment as 
organisms are at present ; and from a geological point of view it 
l)ecomes evident that evolution has been making its way through 
the conditions of environment from the beginning. Generalized 
or archaic tvpes are usually as rare in fossil groups as among liv- 
ing forms. As for example in various groups of gymnosperms, 
the first known forms are as highly specialized as any which 
come later. It is probably safe to say that the conditions of 
environment may and do act as determinative factors in the 
evolutionary process but they are not the cause of the process. 
The three series of plants may be characterized as follows: 
A. Tii.\i.lophyta. Thallophytes. (iO, ()()() known living species. 
The lowest plants; tyjhcally water plants but the majority now with- 
out chlorophyll and living as parasites or saprophytes in aerial conditions; 
plant body a thallus, unicellular, ccxnobioid, or multicellular, usually fila- 
mentous, very minute to gigantic in size; all gradations from the lowest 
nonsexual plants to plants with complete sexuality and often with an 
alternation of generations but the sporo])hyte or nonsexual generation 
always small and not typically developed, the gametophyte being the 
plant ; oosphere when present never prorluccd in an archegonium but in a 
simple oogonium. 
