CH. Xl] BEAN-FLOWER. 149 



side of the flower 1 . If however the flower is split into two 

 by a median section in the plane of the paper, it will be 



FIG. 67. 



FLOWER OF THE SWEET PEA. 



S, standard or vexillum. W, wings or alse. 



.K", keel or carina. (7, calyx. 



(The flower had been preserved in alcohol, hence the keel was visible 

 through the semi-transparent wings.) 



divided into similar halves; it is in fact symmetrical 

 about a median plane which, in the natural position of the 

 flower, is a vertical plane. 



The sepals, as mentioned above, are united into a 

 tubular calyx the edge of which bears five teeth, and 

 these indicate the number of coherent parts forming 

 the calyx. When the calyx has been dissected off, the 

 parts of the corolla are thoroughly exposed. The upper- 

 most petal is the standard or vexillum, whose narrow 

 horizontal base covers over the bases of the other petals, 

 and whose broad apical part stands obliquely upwards. 

 The name standard has been given to this petal because 



1 The flower of the bean, sweet pea, clover and other allied plants is 

 said to be papilionaceous because its irregularity gives it a fancied 

 resemblance to a butterfly. 



