FIELDBOOK OF ILLINOIS WILD FLOWERS 



because the projections are mostly prominent at the ovary, such 

 an ovary is commonly spoken of as lobed. 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 axial attachment to the arrange- 

 ment. Each unit pistil is then a carpel 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 fj'ee 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 style^ 

 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 Ji lament, which bears the principal part of the stamen 

 — the anther, e, or structure in which the pollen grains are 

 formed. Occasionally the filament may be lacking. Anthers have 

 various forms, the most common showing in cross-section tour 

 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 iiicliided. 



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 



