This order contains ten British genera.

Erica tetralix (the Cross-leaved Heath) has been well described by Dr. Ogle (Popular Science Review, April 1870). The flower is in the form of a bell (Fig. 93), which hangs with its mouth downwards, and is almost closed by the pistil, and stigma (st), which represents the clapper. The stamens are eight in number, and each terminates in two cells, which diverge slightly, and have at their lower end an oval opening. But though this opening is at the lower end of the anther cells, the pollen cannot fall out, because each cell, just where the opening is situated, rests against the next anther cell, and the series of anthers thus form a circle surrounding the pistil and not far from the centre of the bell. Each anther cell also sends out a long process (pr, pr), which thus form a series of spokes, standing out from the circle of anthers. Under these circumstances, a bee endeavouring to suck the honey from the nectary cannot fail firstly to bring its head in contact with the viscid stigma (Fig. 93,st) and thus to deposit upon it any pollen derived from a previous visit; and secondly, in thrusting its proboscis up the bell, it inevitably comes in contact with one of the anther processes,pr, which then acts like a lever, and dislocates the whole chain of anther cells, when a shower of pollen falls from the open anther cells on to the head of the bee.

Flower of Erica tetralix.

Fig. 93. - Flower of Erica tetralix.

Stamen of ditto.

Fig 94. - Stamen of ditto.

Erica cinerea agrees very closely with E. tetralix. In Erica (or Calluna) vulgaris (the Common Heath), on the contrary, where the flowers are, in their natural position, more horizontal, the stamens and pistil incline upwards, so that insects press their proboscis under them, and in this manner the pollen is less likely to be wasted, than if they were central as in E. tetralix. In Erica vagans(the Cornish Heath), E. carnea, and E. ciliata, the anthers have no appendages.

In the allied genus Vaccinium there is an arrangement similar to that in Erica, but the anther cells are closed, not by touching one another, but by resting against the style, so that the style itself closes the openings until the anthers are disturbed by the proboscis of the bee. V. uliginosum is much larger than V. Myrtillns, and consequently more conspicuous; V. Myrtillus, on the other hand, has the compensating advantage of being richer in honey.

The curious, brown-coloured, nearly leafless Mono-tropa (Yellow Birds-nest), differs very much from the rest of the order.