SIMPLE THALLOPHYTES WITH SPERMATOPHYTES 293 
some plants that are not true Ferns. The Pteridophytes made 
much advancement in developing tissues and organs. They 
have roots, stems, and leaves, and for this reason are regarded as 
more highly developed than the Bryophytes. 
The Spermatophytes are the Seed Plants. With this group we 
are most familiar, since to this group belong the trees, shrubs, 
and most of the familiar herbaceous plants. It is the seed, which 
is one of their contributions to evolution, that makes many of 
them so useful. In this group occurs the greatest display of 
tissues and organs. 
The Spermatophytes consist of two subdivisions, Gymnosperms 
and Angiosperms: 
The Gymnosperms (Gymnospermae), as the term signifies, do 
not have their seeds enclosed. These are the evergreens, such 
as Pines, Cedars, Spruces, Hemlocks, Firs, etc. 
The Angiosperms (Angiospermae), as the term signifies, have 
their seeds enclosed. This refers to the enclosing of the seed in 
an ovary. Nearly all of the cultivated plants belong in this 
group. They contribute the fruits. 
A Comparison of Simple Thallophytes with Spermatophytes. — 
One striking difference between the simplest Thallophytes and 
the Spermatophytes is in the number of cells of which the plant 
is composed. The simplest Thallophytes are unicellular, while 
the Spermatophytes are extremely multicellular. A second 
striking difference between the plants of the two divisions is in 
the differentiation and specialization of cells which are thereby 
fitted to perform special functions. In unicellular Thallophytes 
one cell performs all of the different kinds of work that the plant 
has to do, while in Spermatophytes there is a division of labor 
among the cells; that is, Spermatophytes have tissues, which 
are groups of cells especially adapted to do particular kinds of 
work. 
As the cells of multicellular plants become differentiated into 
tissues and thus specialized in function, they lose the ability to 
exist independently. Many unicellular plants can live inde- 
pendently of other cells, but in Spermatophytes, the life of a 
cell in most cases depends upon the proper adjustment of the cell 
to the vital processes of other cells of the plant body. Thus the 
ability of a cell to perform many functions is lost in becoming 
adapted to perform one function well. 
