610 



WEED FLORA OF IOWA 



Fig. 467 I Fig. 467 II Fig. 467 III Fig. 467 IV 

 Fig. 467. I. Flower of Ground Ivy with statnens differing in length. II. Mallow 

 with monadelphous stamens. III. Orange with polydelphous stamens. IV. 

 Clover with diadelphous stamens. 



(After Thomfi.) 



Relation of the attachment of floral envelopes and stamens to the 

 pistil. — An examination of the floral sets in shepherd's purse {Gwp- 

 sella) or mustard {Brassica alba) will show that sepals, petals and 

 stamens are inserted on the receptacle below the ovary. This flower 

 is hypogynous (i. e., parts under the pistil). When the petals and 

 stamens are joined to the calyx, the flower is perigynous (i. e., parts 

 around the pistil). In such flowers as the evening primrose and 

 those of the composites, the calyx is adherent to the ovary and the 

 corolla seems to arise from the top of the ovary. Such a flower 

 is said to be epigynous (parts on the pistil). 



Fig. 468. Perigynous flower of the Rose. 

 (After Thomfi.) 



Arrangement of flowers (inflorescence) . — ^Flower arrangement 

 is of three classes; namely, indeterminate, when the flowers arise 

 laterally and successively as the floral axis elongates; determinate, 

 when the flowers arise from the terminal buds and thus check the 

 elongation of the floral axis; and mixed, when these two are com- 

 bined. 



