yNo. 17] FLOWERING PLANTS AND FERNS 1G 
INTRODUCTORY. 
Plants.—The ordinary conception of a plant is that of a 
vegetable organism having three easily recognizable parts in- 
timately related and mutually dependent. These parts are: 
Leaf, Stem (a stalk or trunk), and Root. We visualize a plant 
as having these three parts, the leaf being a flattened green 
organ spread out in the lght and air, the root, a fibrous or 
cylindrical branched organ reaching down into the soil, and 
the stem a more or less stout and often woody vertical shaft 
ecnnecting the other two organs. 
The positions and relations of these three parts are not 
accidental. The leaf must be spread out in the air and light 
in order to perform its functions of elaborating food for growth 
and reproduction of the plant, this being done through the 
action of the sunlight upon the green coloring matter of the 
leaf. The root sinks into the soil, gaining a firm support for 
the rest of the plant, and at the same time, through its myriad 
ramifications reaches out and absorbs abundant moisture and 
plant food from the soil in which it is embedded. The stem, 
which in herbaceous species is often called the stalk, and in 
trees, the trunk, supports the leaves and lifts them into the 
air and light, at the same time connecting them directly with 
the root system through an intricate system of conducting 
yaseular tissue, Which makes up the whole of the stem of herba- 
ceous plants, and all except the heart wood and corky bark 
of trees. 
It will thus be seen how each part of the plant has its own 
specific work to perform, and how they are all interdependent 
and necessary to carry on the life of the plant. 
While the picture drawn is that of the normal plant with 
which we are familiar, the mass of plant life is so great and the 
conditions under which plants grow are so diverse, that there 
aré more species which do not answer in full to this description 
than of those which do. Many desert plants have no function- 
ing leaves, although in such cases some part of the stem per- 
