Page:Popular Science Monthly Volume 53.djvu/784

760 remote date is clearly evidenced by the great development of peculiar species of continental genera. Moreover, Saporta proves that types now found only in the Canaries (or perhaps also in Madeira, the Azores, or Cape Verds) existed in Europe in the Tertiary period. Such are the native laurel, viburnum, and pine. The persistence here of these ancient types speaks strongly for the constancy of the climate—to-day a strong attraction to invalids—for the average summer and winter temperature hardly differ ten degrees.

The great age of the archipelago is further indicated by the marked individuality of the flora of each island. The species have had time to develop in various directions under the influence of the different conditions to which they have been exposed, and the difficulty of obtaining foothold in the rocky, volcanic soil (pointed out by Christ) has doubtless often prevented the intermixture of the parent and derivative forms, so assisting in the formation of new species. For it must have been only rarely that the seeds or fruits brought from one island to another, or from the mainland, have found themselves in places favorable to development. So speciesmaking has progressed, and as a consequence we find Teneriffe with twenty-seven species known from no other region. Grand Canary with seventeen, Palma with eleven, Gomera with ten, Hierro with three. Fuerteventura and Lanzarote, on account of their greater proximity to the African coast, have a somewhat more continental aspect of vegetation than the more westerly members of the group. They have together thirty-two species which are either confined to them or found very seldom on any of the other islands. Other peculiar species are common to two or three islands only.

The soil is very rich. With irrigation three harvests a year are regularly gathered on Canary and Teneriffe. The water supply is largely kept up by the cloud belts, which even in the driest seasons form almost daily over the higher mountains, feeding the springs there which are the life of the land. But, as has already been said, the rocky, volcanic nature of the coast forbids the entrance of many plants, and this fact has had great influence on the character of the flora. The craggy hills and stony shores have a decidedly desert aspect, and adaptations to drought in the form of fleshy, hoary, and coriaceous leaves and stems abound. Euphorbias take the place and have the appearance of the cacti of American deserts. Fleshy Crassulaceæ of the Sempervivum group are more abundant here than in any other part of the world. There are twenty-two species of them which are found nowhere else. Such fleshy plants are not confined to the volcanic wastes and shores. They project from the