410 A. HESSELBO 



Haplozia cremilata is in Iceland a decidedly warm-soil species which 

 is hardly absent from any hot spring, whether sulphurous or alkaline. 

 It grows there in abundance on warm clayey flats which have a tem- 

 perature of 20 -35, near Myvatn even at a temperature of about 40. 

 It occurs far more rarety on peaty soil, and then only scantily. Curi- 

 ously enough, these habitats, also, are situated in districts where there 

 are hot springs. Near Laugarland, for instance at the edge of the 

 marsh, there is a small spring with lukewarm water, but the heat from 

 it can exert no influence on Haplozia cremilata, nor does the latter 

 occur in the immediate neighbourhood of the spring. 



This species varies considerably in colour, size, thickness of the 

 cell-walls and as regards the leaf-margin. In the low, reddish-brown 

 forms which grow on warm ground nearest to the hot water the cell- 

 walls are more highly thickened , and are especially distinctly collen- 

 chymatous, while the more vigorous, green forms which grow at some 

 distance from the spring on more boggy ground, among other Bryo- 

 phyta, have thin-walled cells which are indistinctty collenchj^matous. 

 The marginal cells are sometimes large and thick-walled, sometimes 

 scarcely larger than the other leaf-cells and then only slightly thickened; 

 in such cases it may be difficult to distinguish the plant from the forms 

 of Haplozia sphcerocarpa and Alicularia scalaris with which it is often 

 found associated. Under high magnifying pow r ers the marginal cells 

 will however always be seen to be somewhat papillose, which is never 

 the case in Alicularia. 



28. Haplozia sphserocarpa (Hook.) Dutn. 



S. Iceland: Grafarbakki near a hot spring (F.)!; Thorlakshver among 

 Catharinea undulatal; Sydri Reykjahver among Oligotrichiim hercynicum !; 

 Laugarvatnshver among Sphagnum cymbifoliuml; Isafjordur on a rocky 

 flat '300400 metres above sea-level)!. 



All the forms found, which are quite sterile, stand slender and 

 erect among other Bryophyta and must doubtless be referred more 

 particularly to the type. 



This species, like its companion Oligotrichiim, has a very peculiar 

 distribution in Iceland, having two such widely different areas of distri- 

 bution as the warm clayey flat with a temperature of 25 -30 and 

 the rocky flat. 



Note. A liverwort is figured in Flora Danica, tab. 2195, under the 

 name Jungermannia pumila; it is recorded to have been found by 

 Morch near Lejra. Lindberg, in his critical revision of the mosses 

 in Flora Danica, refers it to Jungermannia ccespiticia, but the specimens 

 are not to be found in the collections. 



29. Haplozia cordifolia (Hook.) Dum. 



Very common and often fruiting richly. It grows especially on 

 rocks, in or by waterfalls; or submerged in rivers, where it sometimes 

 covers large surfaces of the firm rocky bottom with its blackish-green 

 mats. But it may also be met with on irrigated gravelly ground or in 



