THE DICOTYLEDONES 1687 



VI. Ribesoideae 



Shrubs with alternate simple leaves and flowers borne in racemes. The 

 gynoecium is inferior and unilocular w'ith two parietal placentas. The fruit 

 is a berry. Ribes. 



Fig. 1546. — Deutzia scabia. Flowering shoot. 



VII. Baueroideae 



Shrubs with opposite trifoliate leaves and simple axillary flowers. The 

 ovary is semi-inferior with two parietal placentas. The fruit a loculicidal 

 capsule. Bauera. 



The Saxifragoideae are the largest and most important of the sub- 

 families and contain some thirty genera and 600 species. Many species 

 are American in origin, occurring especially in the Andes. Certain genera 

 are widely distributed, as for example Astilbe, which occurs both in eastern 

 Asia and also in North America. 



The pollination mechanism is typically entomophilous and we will 

 consider in detail the mechanism in the genus Saxifraga. This genus is the 

 largest, containing at least 325 species which are distributed on the 

 mountains of the Arctic and north temperate regions and also in the 

 Andes. In colour the flowers may be white, yellow or spotted with pink. 

 The nectar is almost always fully exposed and secreted on the outer walls 

 of the ovary. In this position it can be reached by short-tongued insects 

 among which flies predominate. Owing to the large number of visitors 

 self-pollination is almost if not entirely impossible, and is made more 

 difficult on account of a more or less pronounced dichogamy. Most of the 

 species are protandrous although a few^ are protogynous. In this latter 

 type the flowers are considerably smaller in the first or female condition 

 than in the second or male stage. After the stigma has shrivelled, the flowers 

 increase to twice the original diameter so that visits paid by insects will be 

 most probably in the order most advantageous for cross-pollination. 



X* 



