THE DICOTYLEDONES 



1861 



hairs. The roots of many species have been shown to be inhabited by 

 endotrophic mycorrhizal fungi. 



The inflorescence is usually racemose, though the number of flowers in 

 the inflorescence is often small. 



The flower (Fig. 1764) is hermaphrodite, regular and actinomorphic, 

 occasionally slightly zygomorphic, usually hypogynous, except in Vaccinium 

 where it is epigynous. 



The calyx is pentamerous or tetramerous, gamosepalous and persistent, 

 and except in Vaccinium hypogynous. 



The corolla is regular or slightly zygomorphic 

 in Rhododendron. It is tetramerous or pentamerous 

 and gamopetalous, usually globose or broadly cam- 

 panulate; imbricated in aestivation and often per- 

 sistent as in Calhina and Erica (Fig. 1765). 



The androecium is composed of either eight 

 or ten stamens, rarely five, as in Azalea. They 

 are obdiplostemonous and hypogynous except in 

 Vaccinium. The anthers possess hornlike appen- 

 dages and open by apical pores or slits. The pollen 

 grains remain together in their tetrads and form a 

 powdery or sticky mass, which often comes out of 

 the apical pore in long strings. 



The gynoecium is composed of four or five 

 syncarpous carpels, forming an ovary with four or 

 five loculi, which is superior except in Vaccinium. 

 Each loculus contains from one to many anatropous 

 ovules with axile placentation. The style is simple 

 but the stigma is either capitate or four- or five- 

 lobed. 



The fruit may be a berry or a capsule, the 

 latter splitting either septicidally or loculicidally. 



The seed is small and contains endosperm. 

 The embryo is also small and straight. 



The family is cosmopolitan in distribution occurring all over the world 

 except in deserts or hot, damp tropical regions. There are about fifty 

 genera containing some 1,350 species. Owing to their number and their 

 social habit, they form a quite characteristic part of the vegetation of certain 

 regions of the world. The sub-family Ericoideae (Fig. 1766) is restricted to 

 Europe and Africa, but these two areas are now separated from one another 

 by the Sahara Desert which contains no species. The Rhododendroideae 

 have their centre of distribution in the Himalayas and south-west China. 

 The Arbutoideae and the Vaccinioideae are found chiefly in north tem- 

 perate regions, having several species with circumpolar distribution. 

 According to Drude the Ericaceae are divided into the following sub- 

 families: 



Fig. 1765. — Erica carnea. 

 Longitudinal section 

 of flower. The anthers 

 are exserted and sur- 

 round the immature 

 stigma. 



