THE DICOTYLEDONES 1655 



6. Roseae. The receptacle is urn-shaped and encloses numerous 

 carpels. It becomes fleshy and bright-coloured and contributes 

 to the formation of the fruit. The plants are mostly shrubs with 

 compound stipulate leaves. Rosa. 



IV. Neuradoideae 



This sub-family contains only two small genera, which are desert- 

 loving herbs with yellow flowers. The five to ten carpels are united with 

 each other and also with the receptacle, which enlarges and forms a dry 

 covering around the fruit. 



I, Neuradeae. The only tribe. Neiirada, Grielum. 



V. Prunoideae 



This sub-family is characterized by the solitary carpel, with a terminal 

 style and a pair of pendulous ovules. The fruit is a one-seeded drupe. 

 The flowers are regular and pentamerous. The stamens may be ten, twenty 

 or more in number. The seed or kernel has a papery testa and contains 

 two large cotyledons. There is no endosperm. The plants are mostly 

 trees or large shrubs with simple undivided leaves, and small stipules; 

 many are evergreen. 



I. Pruneae. The only tribe. Pninus, Nuttallia. 



VI. Chrysobalanoideae 



This sub-familv dift'ers from the last in that the style is basal and the 

 ovules are ascending. The flowers frequently show signs of zygomorph} 

 and the plants are mostly tropical evergreen trees or shrubs whose chief 

 centre of distribution is South America. This sub-family is held to show 

 a connecting link between the Prunoideae and the Leguminosae. 



1. Chrysohalaninae. The flowers are nearly regular. Chrysobalanus, 



Parinarium. 



2. Hirtellmae. The flowers are definitely zygomorphic. Hirtella, 



Acioa. 



Space will not allow us to consider all these genera separately nor to 

 consider each of the tribes in detail. We may however review those pollina- 

 tion mechanisms which are most typical of the family as a whole. 



The Rosaceae show a wide range of pollination mechanisms, from 

 anemophily to very specialized flowers suitable for pollination only by 

 particular kinds of insects. Some flowers, as for example those of Alchemilla, 

 are insignificant and unattractive while in others the flowers are large and 

 conspicuous like those of most species of Rosa. The form of the inflor- 

 escence is very varied even within the same genus. Many flowers 

 secrete nectar from an annular ridge on the surface of the receptacle but 

 the quantity varies greatly. In some species of Ruhiis for example the 

 quantity is large while, at the other extreme, in Potentilla it forms a scarcely 

 perceptible film, 

 u* 



