116 SUMMER FLOWERS. 



longer than the perianth^ and three styles which are united at 

 their base, surmounting a free ovary with a single ovule. The 

 fruit is a small triangular seed-like nut, enclosed in the per- 

 sistent perianth. 



The family of the Aristolochiaceous plants is another of 

 these Monochlamydeous groups. It is represented by the 

 Common Birthwort,"^ a South European plant, naturalized 

 among ruins and in stony rubbishy places in the east and 

 south of England. This is a perennial, with a root creeping 

 so extensively underground as to become a rather ti'oublesome 

 weed in situations which are congenial to it. The stems are 

 erect, two to three feet high, several often springing up in a 

 tuft, simple, striated, clothed with stalked, broadly heart- 

 shaped leaves, reniform at the base. The flowers are yellow, 

 collected in little groups in the axils of these leaves,, clustered, 

 or aggregated, as it is called ; they are tubular, erect, or a 

 little arching, globosely tumid at the base, and with a long 

 slender slightly widening tube above, the upper side of which 

 is prolonged into an oblique ovate concave emarginate limb. 

 Within the globular portion at the base of perianth, are placed 

 the anthers and stigmas : the latter being six-lobed, ray-like, 

 terminating the short thick style, around which are fixed the 

 six sessile anthers. The fresh plant when bruised has a strong 

 disagreeable smell, resembling that of Elder. The tumid 

 part of the corolla is covered inside with stiff hairs pointing 

 downwards. When expanded, the flowers are frequently 

 visited by a little insect, called Tipula pennicornis, which enters 

 them, and is prevented by the hairs from making its egress 

 until it has brushed off the pollen from the anthers on to 

 the stigma: "the perianth then withers, the hairs become 

 flaccid, and the insect makes its escape.^' This genus is one 



* Aristolochia Clematitis — Plate 19 B. 



