278 THE JOUUNAL OF BOTANY 



The older records of Hooker, Lindsay, Carroll, etc., are alluded to 

 without enthusiasui. About half the text is devoted to a systematic 

 enumeration of the Eryophyta, the numbers of which are as follows: — ■ 

 Hepatic* 90, Sphagnales 20, Musci veri 325. Among the mosses 

 three new species and three new varieties are described and figured ; 

 and critical notes of some length are appended to several difficult 

 species. The habitats, plant-associations, and distribution are treated 

 w^ith much care — as, indeed, is necessary in ca?e of a country where 

 such extremes of temperature occur — from glacial ice to boiling 

 springs. 



It is the ecological side of Mr. Hesselbo's work that is of prime 

 importance and interest. The long chapter on the Bryophyte Com- 

 munities is divided into the Lowland Formations and the Vegetation 

 of the Mountain Heights. But while the moss-formations of the 

 highlands, and of the heaths, rocks, tuff rocks, and lava-fields, are 

 carefully summarised and are of great value and impoi-tance, it is 

 the conditions that prevail near the hot springs that afford the 

 principal novelty for the British bryologist. 



The vegetation of bogs is entirely dift'erent from that of ground 

 which is inundated or saturated by the pure water of running streams ; 

 for the bog- water is stagnant, contains humic substances, lacks aeration, 

 and is warmed by the sun ; whereas spring-water is clear, contains 

 oxygen and carbonic acid, and has a very low summer temperature 

 {-iP to 6° C). Mr. Hesselbo has much to say about the vegetation 

 characteristic of the different sorts of bogs and streams. But Iceland 

 also abounds in hot springs, and these are of two kinds — the alkaline 

 and the sulphur springs. The alkaline springs occur where no recent 

 volcanic activity has been manifested ; they contain pure clear water 

 which often deposits siliceous sinter, and are always surrounded by a 

 luxuriant vegetation. The sulphur springs are most numerous where 

 volcanic activity is still felt ; they contain sulphuretted hydrogen and 

 deposit sulphur ; and the soil around them is much decomposed by 

 the acid vapours evolved, and is turned into a red or yellow clay ; 

 the vegetation around is very scanty. The Great Greysir falls into 

 the second category; and it is interesting to note that the bread for 

 the neighbouring farmhouse is baked in pots buried in the hot soil. 



The vegetation of these warm grounds dej^ends upon the chemical 

 nature of the water and of the escaping vapours and upon the con- 

 dition of the soil. Where the water is free from sulphuretted 

 hydrogen, and the surroundings are boggy, and warm vapours are 

 evolved, a broad belt of deep Sphagnum cushions Avith a temperature 

 as high as 50° C. may occur, the most frequent species being 

 8. 23(tpiIIosnm. And, as a rule, scattered in the cushions are found 

 a strong fruiting form of Polytriclnim commune, Hypmim strami- 

 neum, Ilylocomium squarrosum, or AeroclacUum cuspidatum. Out- 

 side the Sphagnum belt, there occurs on warm boggy soil (tem. 25°- 

 30° C), a moss carpet chiefly com])osed of Hypnitm imponens and 

 H. Lindhergii, with H. stramineiim, Ilylocomium squarrosum. 

 Acrocladium cuspidatum, Thuidium. delicatuhtm, and numerous 

 other bog-mosses, such as Hypnnm revoJvens, H. molluscum, 

 Catoscopinm nigritum, Fissidens osmundoides, Scapania irrigua. 



