THE DICOTYLEDONES 1785 



aerenchyma. If the plants are grown on land this aerenchyma is not 

 produced. 



Another marsh genus is Ludwigia, which is represented in Britain by a 

 single very rare species. 



The genus Oenothera (Fig. 1677), the Evening Primrose, has gained a 

 reputation in genetical studies on account of the work done on the theory 

 of mutations. De Vries was the first to demonstrate the existence of 



Fig. 1677. — Oenothera biennis. Inflorescence. 



mutation from his study of Evening Primrose in Amsterdam. Later Gates 

 and others investigated very elaborately the cytology of the group and 

 attempted to relate this cytology with the genetics. The subsequent 

 discovery that many of the species studied so carefully were natural hybrids 

 tended to discountenance some of the work though it is still looked upon as 

 of considerable importance. O. biennis and several other species open their 

 large bright yellow flowers at dusk. They emit scent in the evenings and are 

 visited by night-flying long-tongued moths. 



Both the genera Clarkio, with eight North American species, and 

 Godetia with twenty-five \\' estern American species, are extensively used 

 in this country as annual bedding plants. 



The genus Fuchsia is essentially composed of shrubs. There are some 

 sixty-five species distributed in South and Central America and in New 

 Zealand. Many have long racemes of flowers in which the calyx is petaloid 

 and bends backwards to expose the corolla. Frequently the two whorls are 

 of diflFerent colours. Many have been cultivated and hybrids have been 

 produced in which the calyx and corolla possess contrasting colours, white 



