450 



NA TURE 



[A/>rtlg, 1874 



T//£ ''CHALLENGER" EXPEDITION 



III. 



St. Vincent, Cape de Verde Islands 



ST. VINCENT, one of the Cape de Verde Islands, 

 noted in the old gazeteers for its wood, water, wild 

 goats, turtles, and saltpetre, was visited by the Challenger 

 in July and August last. From a record of this visit we 

 gather the following particulars about the island itself 

 and of the plants growing there. The island is small, not 

 more than twelve miles by six, comparatively flat in the 

 centre, but surrounded by higher land. This range of 

 high land is divided by a series of deep valleys, forming 

 ridges which are again divided into transverse valleys. 

 Most of the hills are from 700 to 1,200 ft. high, but one in 

 the south is over 2,200 ft. high. St. Vincent is some- 

 times visited by long periods of drought, extending occa- 

 sionally to a year's duration, during which time the whole 

 island has a parched, sterile appearance. The most 

 abundant plant in the island is Lavandula rotundifolia 

 Bth., which forms small thick bushes ; there is also on 

 the summits of the higher hills Euphorbia tuckeyana, 

 Steud., and on the sandy plains as seen from the vessel in 

 Porto Grande, reaching inland from the shore, wer: 

 dense masses of bushes of Tamarix gallica. In one 

 spot, sprmging up from amongst these bushes, was the 

 well-known tamarind tree {Ta?narindiis indica L.), so valu- 

 able both in the East and West Indies, for the sake of the 

 agreeable acid pulp contained in the pod, which when 

 preserved in sugar forms " Tamarinds '' of commerce. 

 Side by side with the tamarind grew Acacia albida Del., 

 and Terminalia catappa L., the first being one of the 

 many spiny acacias found on the African continent, where 

 it fomrs a large straggling branching tree, with straight, 

 stout spines, sometimes \ in. long. The Terminalia is a 

 native of India, but has been found in Upper Guinea, 

 though probably not indigenous. The seeds are almond- 

 shaped, white, and of an agreeable taste. In the plains 

 Tribiilus cistoides L., a spreading prostrate or decumbent 

 plant, occurs in great abundance, as also a small gr^ss. 

 Nearly all the vegetation, however, had a shrivelled, 

 dried-up appearance, with the exception of the lavender, 

 upon which a few fresh green leaves were to be seen. 

 The effect of rain in changing the aspect of vegetation on 

 this island is said to be almost instantaneous, not only in 

 bringing out the young foUage of perennial plants, but 

 also in causing a thick carpet of seedlings to spring up. 

 Though the hill slopes and the lower parts of the valleys 

 are in some parts of the island covered with a thick grass, 

 the drought causes it to become so dry that goats and 

 cattle frequently die from sheer starvation. 



On the Green Mountain, at an altitude of about 200 ft. 

 above the level of the sea, the gardens contained pump- 

 kins, sugar-cane, a small kind of date-palm, and maize ; 

 cotton bushes also grew in the neighbourhood. At 

 another 500 ft. there were Euphorbias and the woody 

 Composites. At 1,000 ft. there were Echium stcnosiplton 

 Webb, in flower ; and at 1,300 ft. occurred patches of 

 moss and marchantia, while at 1,700 ft. Statice jovi-barha 

 Webb was abundant. The Lavandula rotundifolia, which 

 is found at the very top of the mountain, has here a very 

 different aspect from that before described, inasmuch as 

 it is green and vigorous-looking. In the south-west of the 

 island, at a height of goo ft., was discovered a single plant 

 of Sarcosteniina daltoni Dene, which grows on the cliffs 

 at St. J ago, almost down to the sea. On the top of the 

 Green Mountain the land is much cultivated with potatoes, 

 tomatoes, pumpkins, maize, and similar plants. The posi- 

 tion is so favourable to the growth of the tomato that it 

 appears to have run wild. The origin of many of the 

 introduced weeds which grow on the mountain is no 

 doubt traceable to the imported seeds of the vegetables 

 just mentioned. 



At an elevation of about 2,000 ft. was a group of agaves 

 planted in the form of a double circle ; many of them had 

 flowering spikes about 10 ft. high. The marked differ- 

 ences of aspoct caused respectively by the trade-winds 

 and the sun, at altitudes suitable for plant growth, are 

 points of much interest, illustrations of which may be had 

 in the fact that Aizoon canariensc L., which grows on the 

 windward and shady side of Bird Rock, nearly down to 

 the sea-level, does not commence till 700 feet or 800 

 feet on the leeward sides of the main island ; the 

 Euphorbias and woody Composites are found at about the 

 same elevation, while on the other side they reach nearly 

 down to the sea. On the windward slopes of the moun- 

 tains, on the southern side of the island, the vegetation 

 commences at a higher elevation, being kept back by the 

 wind becoming heated and dry from its passage across 

 the hot central plain. 



Sinapidendron vogelii Webb, a cruciferous under- 

 shrub, with yellow flowers, grows on the cliffs on the 

 weather side of the island ; and Samoius valeraiidi 

 L., known to us as the brookweed or water pim- 

 pernel, an erect plant, from 8 in. to loin, high, growing 

 in marshy places or near springs, was also seen, but only 

 in a single isolated patch near a small stream. This plant 

 is remarkable for its very wide geographical range, being 

 found in almost ever)' country where the soil is wet and 

 gravelly, and though seen only in this one spot in St. 

 Vincent, it grows abundantly in St. Jago by the stream 

 in St. Domingo Valley. 



As seen from the sea, the rocks of St. Vincent present 

 a singular appearance, owing to the presence of a thick 

 incrustation at water-mark of masses of calcareous alga:, 

 which either follow the forms of the rocks, or occur in 

 rounded masses, their delicate tints of white, light pink, or 

 cream colour, considerably heightening the effect. These in- 

 crustations are frequently bored by Lithodomus candigerus 

 and other molluscs, and small sponges and Bi-yozoa 

 occupy the cavities between them and the rocks. 

 St. Paul's Rocks 



The isolated rocks known as St. Paul's Rocks lie to the 

 north of the equator about 1°, and in longitude 29° 15' W., 

 nearly midway between the South American and African 

 coasts. They are in truth mere rocks, not more than a 

 quarter of a mile long, and rising to a height of from 50 to 

 60 ft. above the sea. They are described by travellers as 

 being quite bare of land- vegetation even to the exclusion 

 of lichens, the only vegetation in fact i being numerous 

 species of algte. 



From an examination made of the rocks during the 

 two days' stay of the Challenger, it seems that the species 

 of algje are by no means numerous, fourteen species being 

 all that were found ; so powerful indeed is the wash of the 

 waves that it seems to be too much even for these marine 

 plants to retain their positions. The water also deepens 

 very rapidly round the rocks, so that it is not likely many 

 species would be found there. 



A similar incrustation of calcareous algre is seen upon the 

 rocks as at St. \^incent. It here forms a deep pinkish 

 white band at tide mark, and is riddled through and 

 through by a small annelid. In some places the colour 

 of the incrustation is white, and above this is a dark red- 

 coloured alg£e, covering the rocks for several feet. At the 

 bottom of the small bay formed by the circlet of rocks 

 and extending out in the sea to a depth of twenty 

 fathoms, is a thick growth of a green-coloured sea-weed 

 {Caulerpa clavifcra Ag.), together with another species 

 of smaller growth. The former is loosened from the 

 bottom by the action of the waves, and is gathered up by 

 the noddies {Sterna stolida) to build their nests. 



A few diatoms and oscillatori.X" occur in stagnant pools, 

 among them being Navicula didyina, Rltabdonenia adria- 

 ticuni and Biddulpltia pulehella. A careful examination of 

 the guano found in the hollows of the rocks showed that 

 no diatoms were present, but fossil fragments of incrus- 



