THE ECOLOGY OP PLANTS. 



429 



In the Ling or Common Heather (Cattuna vulgaris) the leaves are 

 very short and arranged in crossed pairs, forming four rows ; the copious 

 branching, minute size of the leaves (2 or 3mm. long, 0'5 mm. broad), 

 and the closely set four rows of leaves at once distinguish this plant 

 from the Heaths (Erica) ; the rosy drooping flowers are in dense spikes ; 

 both K and C are rosy and 4-lobed, the corolla being shorter than the 

 calyx ; each of the 8 anthers has 2 appendages and opens by 2 pores at 

 the tip ; a bee entering the flower comes against the anther appendages, 

 shakes the anthers, and brings a shower of pollen down on its head, 

 which had previously touched the stigma ; ovary 4-chambered with 

 numerous ovules ; capsule enclosed by persistent corolla which fades to 

 brown after fertilisation has occurred ; capsule ripens in autumn and 



Fig. 177. Sprig of Cross-leaved 

 Heather (Erica tetralix). 



Fig. 178. Vertical Section 

 of Flower of Erica tetralix. 



opens in spring by 4 slits, the small seeds being scattered by the wind ; 

 the flowers are doubtless largely wind-pollinated ; the pollen is light 

 and dry and escapes in clouds when the plant is shaken violently. 



In Bell Heath (Erica cinerea) the leaves are larger than in Ling, 

 being about 6 mm. long and 1 mm. broad, and are arranged in threes 

 and not so crowded on the stems ; flowers red-purple, larger and less 

 densely arranged than in Ling, sepals green, corolla bell-shaped. The 

 Cross-leaved Heath (E. tetralix, Figs. 177, 178) is lower and less 

 gregarious than Ling and E. cinerea, and is chiefly found in the 

 moister places in small groups ; leaves in fours, downy below, with a 

 wide slit, much less rolled up ; flowers large, pinkish, in small clusters 

 at ends of branches. The Bilberry ( Vaccinium myrtillus) belongs to 

 the same family as Ling and the Heaths (Ericaceae), but differs in 

 having broad thin deciduous leaves which fall off early, the numerous 

 green angular branches carrying on photosynthesis when leafless ; 



