THE AZORES 



411 



Teneriffe possess many features in common, the plants that have 

 found a home on their summits differ greatly. We have seen that 

 the plants which have reached the summit of the great cone of Pico, 

 the Heather (Calluna vulgaris), the Heath (Menziesia polifolia), the 

 Thyme (a variety of Thymus serpyllum), the grasses, etc., have all 

 climbed up from the moors below. This would have been impossible 

 either on Teneriffe or Madeira, on account of the absence of moors 

 of this description. Yet in the queer little gathering of half a dozen 

 native plants, which Lowe describes as having found a refuge on 

 the rocky crags of the summit of Madeira, there is a small effort 

 in this direction. After removing from his list Cerastium tetrandrum 

 (Curt.), as probably an introduced weed, there remain Arenaria 

 serpyllifolia, Erica cinerea, Viola paradoxa, Armeria maderensis, 

 and Avena marginata, the three last being first described by Lowe 

 as peculiar to the island. Coming to the scanty vegetation of the 

 high levels of Teneriffe, it is to be again observed, that apart from 

 the perennial herbs (Arabis albida, etc.) it is the Retama broom 

 (Spartocytisus nubigenus) that gives a character to the pumice-stone 

 plains of the Canadas between 7000 and 9000 feet above the sea, 

 a leafless shrub that climbs the steep lava slopes of the terminal 

 cone to a height of 11,000 feet. The history of the Retama in this 

 elevated area is implied in a remark of Hooker, that its Moorish 

 name has come to be used by botanists for a small group of brooms, 

 containing a few nearly allied species, that are widely spread through- 

 out the region extending from Spain to the Canary Islands (Marocco 

 and the Great Atlas, p. 27). A Violet, known as Viola teydensis and 

 peculiar to the peak, clings to the soil at the upper edge of the Llano 

 de la Retama, as the pumice-stone plains are called. Above this 

 level, writes Johnson (Encycl. Brit. 9th edit. IV., 797), there is nothing 

 but a little lichen. 



We have remarked that the peculiar feature of the summit vegeta- 

 tion of the great cone of Pico, as compared with the Peak of Teneriffe 

 and with Madeira, is that it is all derived from the moors below. 

 This brings us to another distinctive feature in the zones of Pico. 

 The wet and dry moors, which are so conspicuous around the middle 

 levels of the mountain of Pico, having been formed at the expense 

 of the upper woods or the Juniper zone, seem scarcely represented 

 on Teneriffe and Madeira, hardly any of their characteristic plants 

 being there present. This contrast is well reflected in the differences 

 in the Sphagnum floras of the three groups, as brought out in Warn- 

 storf's monograph on the Sphagnaceaz (Das Pflanzenreich, 1911). 

 Whilst in the Azores there are nine known species of Peat-mosses, of 

 which two are peculiar to the group, there seems to be in each case 

 only a single wide-ranging species in Madeira and the Canaries, a 

 fact that points to prevailing unfavourable conditions for the develop- 

 ment of Sphagnum moors in those islands. 



The Plant-Stocking of the Macaronesian Islands. — But to 

 return to our general comparison of the floras of the Macaronesian 

 islands, there is a wider outlook of the question, such as Hooker 

 presented in his Lecture on Insular Floras (1866), and in his discussion 

 of the Canarian flora in his later work on Marocco (1878), and such 



