PLANT STRUCTURES 
7 
There are numerous terms that are used to describe the apexes 
and bases of leaves, but we can dispense with most of these and the 
few that we find it necessary to use will be readily understood 
as we come to them. 
Flowers— A complete flower consists of four sets of parts (pi. IY). 
Beginning at the outside, the first set consists of leaflike parts which 
are usually green and are called sepals. The sepals may be entirely 
separate or more or less grown together and all of the sepals collec¬ 
tively, whether united or not, make up the calyx. The parts of the 
second set of organs are also more or less leaflike, but usually some 
other color than green and are called petals. These, like the sepals, 
may or may not be united, and they collectively make up the corolla. 
The parts of the third set are called stamens. In most cases they are 
not at all leaflike. Each one consists, as a general rule, of a stalk¬ 
like portion called the filament and a headlike portion called the 
anther. Within the anther are found the numerous, minute pollen 
grains that contain the male elements of the plant. The number of 
stamens, varying from one to many in the different kinds of plants, 
is very important in the identification of plants. Finally, the fourth 
set of parts consists of one or more pistils, each pistil consisting, or¬ 
dinarily, of three parts: a more or less slender portion called the 
style; an enlarged basal portion called the ovary within which 
are the ovules that contain the female elements and that later may 
develop into seeds; and a somewhat enlarged upper end to which 
pollen grains readily adhere and which is called the stigma. 
Any one or more of these sets of parts may be missing, in which 
case the flower is said to be incomplete. More important to us, how¬ 
ever, than the terms complete and incomplete are the terms perfect 
and imperfect. Any flower that has both stamens and pistils is per¬ 
fect regardless of whether it has a calyx or a corolla or not, while 
if either stamens or pistils are lacking the flower is imperfect. This 
is due to the fact that the stamens and pistils are the organs that are 
directly concerned in reproduction. 
Regular and irregular are also terms that are quite important. 
These refer especially to the corolla. If the petals or parts of the corolla 
are all the same size and shape the flower is said to be regular, while 
if they differ in either size or shape, or both, the flower is irregular. 
The stem of a flower is called a pedicel, and a stem bearing a 
cluster of flowers is called a peduncle. The end of the pedicel to 
which the parts of the flower are attached is called the receptacle. 
Plate Y illustrates the various arrangements of flowers on the stem. 
HOW TO USE THE KEY 
Approximately 1,050 species of plants are included in this book. 
Obviously, if it were necessary to search through the entire 1,050 
