FIELDBOOK OF ILLINOIS WILD FLOWERS 
because the projections are mostly prominent at the ovary, such 
an ovary is commonly spoken of as /obed. Within the ovary at 
the base of each pistil are one or more small bodies, called ovules, 
attached to a mass of tissue which, no matter what its location 
in the ovary, is called the placenta. If this tissue is part of or an 
outgrowth from the wall of the ovary, the ovule attachment is 
said to be parietal. In the compound ovary the placenta of 
each unit pistil may appear to have been pressed so closely to 
its neighbor that fusion occurred, to produce a united column 
in the middle of the structure. This column or axis to which the 
ovules cling gives the name of axia/ attachment to the arrange- 
ment. Each unit pistil is then a carpe/in the compound pistil, and 
its walls form partitions in the compound ovary. If we imagine 
that in some flowers these partitions disappear so that the several 
carpels coalesce into a single compartment, the placentas will 
be left as a column by itself in the center, and to this form is 
given the name free central placenta, which is the type common 
to the Pink family. At the upper end of the pistil is a portion, 
c, usually enlarged, which is called the stigma. This is usually 
somewhat sticky and it serves to receive the pollen. The sty/e, 
b, merely connects stigma and ovary; in a few cases it is lacking 
and in others it may be branched as further indication that the 
pistil is compound. 
STAMENS, PETALS AND SEPALS 
Stamens.—Next outside the pistil or pistils is a set of organs 
called stamens, which vary greatly in number among species. 
A stamen, fig. 4 II, usually consists of a stalklike portion, d, 
called the fi/ament, which bears the principal part of the stamen 
—the anther, e, or structure in which the pollen grains are 
formed. ee ciclle the filament may be lacking. Anthers have 
various forms, the most common showing in cross-section four 
rounded masses of pollen-forming cells. At a later stage, f, 
two of the walls between these pollen cells break down to loose 
the pollen grains in two chambers or pollen sacs, one on either 
side of the anther. Stamens may have long filaments and extend 
beyond other parts of the flower, then they are spoken of as 
exserted; when they do not extend they are included. 
Petals—Outside the stamens is a leaflike whorl of organs 
which are rarely green and more often white or highly colored. 
These are the petals, which make up the corolla, fig. 4 III h. 
13 
