32 ELEMENTS OF STRUCTURAL BOTANY. 



differing very widely in external appearance the Locust- 

 Tree and the Clover, for example but exhibiting in the 

 structure of their flowers so marked a similarity that their 

 relationship is beyond question. The characters by which 

 the Order is distinguished are chiefly these : 



1. The corolla is more or less papilionaceous, and is 



inserted on the base of the calyx (perigynous). 



2. The stamens, almost invariably ten in number, are 



also perigynous, and nearly always diadelphous. 



3. The pistil is nearly always a legume, that is to say, 



it is a single carpel which splits into two pieces at 

 maturity, like the pod of the Pea or Bean. 



4. The leaves have stipules, and are nearly always com- 



pound, that is, of several distinct leaflets. 

 Plants which may be compared with the Pea are Eed 

 Clover, White Clover, Sweet Clover, Medick, Locust-Tree, 

 Bean, Vetch, Lupine, Sweet Pea, &c. 



44. Great Willow-herb. This plant is extremely 

 common in low grounds and newly-cleared land, and you 

 may easily recognize it by its tall stem 

 and bright purple flowers. 



Observe the position of the flowers. 

 In the three plants first examined we 

 found the flowers at the end of the 

 stem. In the Willow-herb, as in the 

 Mallow, they spring from the sides 

 of the stem, and immediately below 

 the point from which each flower Fig. 40. 



springs you will find a small leaf or bract (Fig. 40). Flowers 



Fig. 40. -Flower of Great Willow-herb. 



