At Bratholt we reached civilisation again, and were presented with some of the lichen from which the orange dye, still used in the island, is obtained.
Between Geysir and Thingvellir we passed through one of the largest forests in the island; the hillsides were covered with birch-bushes, and in places they were quite six feet high; usually they did not rise to a height of more than three or four feet, and the topmost branches became entangled in our legs as we rode among the bushes. All four species of birch were noticed, and the scent of the bruised leaves was very pleasant. By way of undergrowth, the ground was carpeted with Geranium sylvaticum, Ranunculus repens, and large patches of Orchis maculata, etc. It was altogether a beautiful spot, and we spent nearly four hours wending our way through it. The river Bruará runs through the middle of this forest.
At Thingvellir Gentiana nivalis was found among other plants.
The rarity of blue flowers in the part of the island visited by us, and indeed throughout the island, was very striking, as the only other blue flowers noticed, besides the gentian, were the Veronicas, and the Myosotis and Viola tricolor found at Akureyri, and Campanula rotundifolia and Pleurogyne rotata, which were found on the east coast on the return journey. Gentiana campestris and G. nivalis were also found on the west coast. White, pale pink, and yellow were the common colours, white being the predominant. The three most common orchids, Habenaria albida, Habenaria viridis, and Plantanthera hyperborea were green and fairly inconspicuous. Perhaps the most striking flowers are the large rose-coloured Epilobium latifolium, which grows on bare islands of stones and black sand in the glacier streams, the yellow Saxifraga Hirculus, and Dryas octopetala, which covers vast tracts of country.
Between Thingvellir and Keykjavik is an extensive Heithi, over which we rode rapidly. There appeared to be no features of any special interest, and as the day was very wet it was not possible to study the flora carefully. On the beach at Reykjavik Mertensia maritima is a fairly common plant.
The hot springs at Hveravellir and other places contain large quantities of algæ, mostly belonging to the blue-green family or Cyanophyceæ. Specimens were collected from various springs at Hveravellir, Kerlingarfjöll, and Geysir, and the temperature of the water in which they were growing was carefully recorded. As I was unable to examine them in detail, I sent them to Professor West of Cirencester, who has worked through my material and published a paper on hot-spring algæ in the Journal of Botany,[2] in which he gives a list of all the algæ we brought back from Iceland.
The highest temperature at which algæ were found was 85° C. (185° F.). Most of the forms found had not been previously recorded from Iceland, and there was one new species belonging to the genus Aulosira, A. thermalis. Full details of these interesting algæ will be found in the paper to which a reference has been given.