[2]These sandhills were revisited by one of our party in the month of June, and then supplied many interesting plants not seen during our first stay at Tangier.
[3]In the Herbarium of the late Mr. Webb, now in the Museum at Florence, the plants gathered by him during his short expedition to Marocco are preserved as a separate collection. Amongst these are some fragments of the Atlantic cedar, which would appear from the accompanying label to have been obtained by him at Tetuan from some native of the Riff Mountains. It is probable that the same tree may be widely spread throughout the unexplored mountain districts of North-eastern Marocco. Gerhard Rohlfs, the only European who is known to have traversed the high mountain region S. of Fez, describing the fine valleys inhabited by the powerful tribe of the Beni M’ghill, says that the prevailing trees were larches of greater dimensions than he had ever seen elsewhere. He declares that he measured several stems from three to four metres in girth, and that such were not uncommon. It is in the highest degree improbable that the larch, which in Europe finds its southern limit in the Pyrenees, should extend to Marocco; and, as Mr. Rohlfs has no knowledge of botany, it is most likely that the tree which called forth his admiration is the Atlantic cedar.
CHAPTER III.
Sail to Algeciras — Vegetation of the neighbouring hills — Comparison between the opposite sides of the Strait of Gibraltar — Return to Tangier — Troubles of a botanist — Fez pottery — Voyage in French steamer — Rabat and Sallee — Land at Casa Blanca — Vegetation of the neighbourhood — Humidity of the coast climate — Mazagan — View of Saffi.
With the previous permission of the Commandant, we sailed from Ceuta in the Government felucca on the morning of the 15th, and had a pleasant run before a south-west breeze, which took us before noon to Algeciras. Our intention had been to return the same day to Tangier, but we found that the ordinary steamer had been taken up to carry sight-seers to a bull-fight at Seville. Resigning ourselves to the delay, we found fair accommodation in an inn upon the quay, and started for a walk over the wooded hills behind the town, not sorry to have an opportunity of comparing the vegetation of the opposite shores at this point where Europe and Africa so nearly meet.
The general aspect of the floras is nearly identical, but there is enough of difference to show that for a long period a barrier has existed sufficient to limit the diffusion of many characteristic species. Of these we found three on the hill near Algeciras—Rhododendron ponticum, Sibthorpia europæa, and Helianthemum lasianthum, a fine species with large yellow flowers, approaching a Cistus in stature and habit. A much longer list of European plants that have not passed into Africa might be made if all the known species found between Gibraltar and Trafalgar were taken into account; but it might with some reason be objected, that our knowledge of the African side of the Strait is too incomplete to speak confidently on this point. On the other hand, however, we may with some certainty assert that comparatively many well-marked species found on the southern side of the Strait are limited to the African shore, and have not been able to spread into Europe. From the accessible materials we find at least thirty-eight species belonging to this category, of which the large majority are species spread over a wide area in Northern Africa.
In attempting to draw inferences from these facts, it is necessary to bear in mind that the region where they occur—the southern part of the Iberian peninsula, and the opposite corner of Marocco—is remarkable for the variety of its flora, and for the large number of distinct species, each inhabiting a very restricted area. To those who suppose that the presence of numerous plants in two neighbouring districts, which are limited to one or the other, but are not common to both, is to be regarded as evidence for the existence of a physical barrier between them, an objector might reply that we have no more right to affirm that it is the prolonged existence of the Strait between Europe and Africa that has prevented the extension of so many species from one continent to the other, than we have to maintain that two neighbouring mountain groups, such as the Sierra Nevada of Granada and the Serrania de Ronda, each possessing a number of peculiar species, must have been formerly isolated by the sea, as otherwise the species would have been intermixed.
In answer to this objection, it may, with some plausibility, be urged that a large majority of the species with restricted areas are mountain plants; that there is much reason to believe that most of these peculiar species did originate within insulated areas, at a time when these were separated by the sea from neighbouring masses, where the conditions of life for each organism must have been somewhat different; and that in a few instances local peculiarities of soil, either chemical or mechanical, may explain the fact that a particular species is limited to a very small district. These considerations do not, however, fully explain the known facts regarding some regions of the earth possessing an exceptional number of peculiar species confined to small areas, the most remarkable of which are Asia Minor, South Africa, South-western Australia, and that which we are now discussing; and in weighing the evidence afforded by the floras of the opposite coasts as bearing on the probable duration of such a barrier as the Strait of Gibraltar, it is best to leave out of account all species that are not known to be widely distributed. Here our very limited knowledge of the flora of North Marocco opposes a considerable difficulty. Subject to such light as future observation will throw upon the subject, it may be said that, so far as mere botanical evidence goes, we should infer that the barrier was not present at the time when the great majority of the existing plants spread into this region; but that it has been established long enough to oppose a limit to the further diffusion of many species that otherwise would, in all probability, be found on both sides of the Strait, thus indicating a period geologically recent, but very ancient as compared with the historic record.
On the following morning we crossed the bay to Gibraltar, and, still finding no means of conveyance to Tangier, endeavoured to console ourselves by botanising on the ‘Rock.’ Later in the day the impatience natural to the British traveller induced us to open negotiations for the hire of one of the numerous tug steamers that make handsome profits by helping becalmed ships through the Strait. The first demand of one hundred dollars helped to moderate our ardour; and, though the more reasonable sum of forty-five dollars was afterwards named by another merchant, we finally decided to remain a second night in Europe, and await the ordinary steamer on the following day.