ILLINOIS NATURAL HISTORY SURVEY MANUAL 1 



Petals, and to some extent sepals, by being joined for part 

 or all of their length, present a variety of forms, regular and 

 irregular. Certain types of joined corollas are tubular^ others are 

 bell shaped. A narrow tube that flares into a wide-spreading 

 border, called the limb^ is salverjorm. If the tube graduates 

 into the border instead of diverging suddenly, the corolla is 

 Junneljorm. The junction of tube and limb is the throat. Flowers 

 whose petals spread out at once, with no tube or a very short 

 one, and radiate like the spokes of a wheel, are wheel shaped. 



Arrangement of the flower organs. — We have seen that the 

 organs are in sets or whorls around the center of the flower, 

 but we will also need to consider the relative heights at which 

 they are attached. 



Fig. 5. — Attachment of the flower parts, a. — Hypogyny. 

 b. — Perigyny. c. — Epigyny. 



The stem or flower stalk that supports a solitary flower or a 

 flower cluster is called the peduncle. The stalk of an individual 

 flower within a cluster is t\\t pedicel. The upper end of the flower 

 stalk, to which the flower parts are attached, is the receptacle. 

 Alteration in the shape of the receptacle produces the three 

 forms of flowers shown in fig. 5. A convex or conical receptacle 

 has the sets of organs placed upon it one above the other, the 

 lowest being sepals, next petals, then stamens and finally pistils. 

 Such a flower is hypogynous^ and the ovary is superior^ a. In 

 other flowers the receptacle is cup shaped and the calyx and 

 corolla are attached to its edge, around the pistil but entirely 

 free from it. Such a flower \^ perigynous ^\i. Finally the receptacle 

 may be concave, enclosing the ovary and grown fast to it. Here 

 the other parts are attached to the receptacle above an inferior 

 ovary, and the flower is epigynoiis^ c. 



Flower clusters — A plant may bear only one flower or it 

 may have several or many in clusters. Each cluster is an 

 inflorescence, of which there may be one or many on the plant. 



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