THE DICOTYLEDONES 1939 



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Fig. 1866. — Myrmecodia echiuata. A young plant showing the 

 early formation of the stem tuber containing the hollow 

 passages in which the ants live. {After Treiib.) 



Hollow swollen internodes occur in the genera Naiidea and Diiroia. 

 In the latter genus, which contains ten South American species, the stems 

 are swollen just below the inflorescence. This swollen region is hollow and 

 entrance is gained by two longitudinal slits. It becomes inhabited by ants 

 which bite through the thin base of the slits to gain admission. In one 

 species, D. saccifera, the ant houses occur in the leaves, where two pear- 

 shaped outgrowths are formed on the under surface. The entrance is on 

 the upper side of the leaf and is protected by a little flap of tissue. 



The origin of the Rubiaceae may probably be found in the Umbelli- 

 florae, which also show tetramerous to pentamerous flowers which are 

 tetracyclic and epigynous, a more or less suppressed calyx, a fleshy disc 

 covering the ovary, anatropous ovules with a single integument and an 

 embryo containing endosperm. 



The Caprifoliaceae (Loniceraceae) are a much smaller family with 

 only twelve genera and about 400 species, most of which inhabit north 

 temperate regions. They are mostly woody plants with decussate leaves 

 and cymose inflorescences of showy flowers (Fig. 1867). 



The flowers are hermaphrodite, actinomorphic or zygomorphic and 

 usually pentamerous but with a reduced number of carpels. The calvx is 

 usually small, consisting of five lobes or teeth. The stamens are inserted 

 on the corolla tube and the anthers are usually introrse. The ovary is 

 inferior, one to five locular, with one to many pendulous ovules. The fruit 

 is a berry or drupe, except in Diervilla where it is a capsule. The seed 

 contains a straight embryo embedded in fleshy endosperm. 



There are a number of well-known genera in this family, among the 

 commonest being Sambucus, with S. nigra (Elder); Viburnum, including 

 V. lantana (Wayfaring Tree), V. opulus (Guelder Rose), and many culti- 

 vated species (Fig. 1868); Synip/iuricarpus, with S. racemosus (Snowberry); 



