THE DICOTYLEDONES 



1821 



The genus Biophytum, containing some sixty tropical species, is interest- 

 ing because of the sensitive, pinnate leaves possessed by many of them. 

 These leaflets bend down when touched, in a way similar to that in Mimosa 

 pudica. Many species of Oxalis exhibit nyctinastic movement. Another 

 genus worthy of mention is Averrhoa, whose two species are trees which 

 are cultivated in the tropics for their berries, which taste much like Goose- 

 berries. They are known as Carambola {A. carambola) and Bilimbi {A. 

 bilimbi) respectively. 



The Tropaeolaceae are a small family with the single genus Tropaeolum 

 (Fig. 1722). There are about fifty species occurring chiefly in South 



Fig. 1722. — Tropaeolum majiis. Garden " Nasturtium ". Left, flower in face view. Right, 



flower in profile showing the spur. 



and Central America (Fig. 1723). Most of them are herbs climbing by 

 sensitive petioles, with compound or peltate laminae. The flowers (Fig. 

 1724) show an advanced character in that they are zygomorphic, with a 

 posterior spur formed by the axis under the posterior sepal, to which two 

 lateral sepals unite to contribute to form the large spur. The embryogeny 

 is abnormal in that the suspensor becomes much elongated and grows 

 out of the micropyle, where it bears two long appendages or haustoria, 

 one of which grows into the tissue of the placenta and absorbs nourish- 

 ment for the developing embryo, while the other grows into the ovary 

 cavity and may serve as an organ of respiration. The embryo and its 

 cotyledons finally fill the seed coat, there being no endosperm. Several 

 species of Tropaeolum are commonly cultivated in gardens. The common 

 garden Nasturtium or Indian Cress is T. majiis; the Canary Creeper 

 is T. peregrinum; while the red T. speciosum also thrives in sheltered 

 positions. It is a tuberous-rooted perennial, as is also T. polyphyllum. 



In the Balsaminaceae there are two genera, Impatiens with about 



