THE DICOTYLEDOXES 



1865 



Nectar is secreted by a swelling at the base of the ovary, and is often pro- 

 tected by erect hairs on the filaments of the stamens. Pollination is effected 

 by humble bees who are forced to crawl over the stamens and stigma to 

 reach the nectar. As the longest stamens project beyond the stigma, 

 automatic self-pollination is possible if insect pollination fails. In many 

 species the pollen grains remain cemented together in tetrads. The tetrads 

 are also loosely held together by threads of viscin. 



The second sub-family, the Arbutoideae, is smaller, containing some 

 250 species distributed among twenty genera. They are chiefly north 

 temperate and Arctic species. The largest genus, Gaultheria, with 100 

 species, occurs in America, from the Andes, through central South America 

 to Chile. A few species, e.g., Arctostaphylos alpina and A. ma-ursi and 



Fig. 1772. — Aibiitiis unedu. Shoot with 

 flowers and fruits. 



Andromeda polifolia, are Arctic or alpine species found in Britain. The 

 Strawberry Tree, Arbutus iinedo [Fig. 1772), inhabits natural woodlands near 

 Killarney. It is one of the group of so-called Lusitanian species found in 

 the extreme west of the British Isles. 



In these genera the flowers are usually homogamous or slightly proto- 

 gynous and nectar is secreted at the base of the corolla. In Arctostaphylos 

 uva-ursi (Fig. 1773) the nectar does not remain in the nectary but collects 

 in ten pits which surround it, in the base of the corolla. It is prevented 

 from running down the petals by the dense covering of hairs which are 

 developed on the filaments of the stamens. The stamens are highly modified. 

 At the base the filament is narrow and tubular, but immediately above it 



