The Botany of Iceland - 01.12.1928, Qupperneq 30

354
JOHS. BOYE PETERSEN
autumnale, which formed pretty, silky, almosl black laj'ers. It is
a characteristic fact that though the ground was fairly moist, no
Diatoms were found here. Presumably they have not been able to
stand the strong manure.
b. Soil Saturated with Urine. (Samples 172, 173).
At the farm IJlfsbær in N. Iceland was a tank with liquid ma-
nure round wliich the ground was quite saturated with urine. Here
was likewise found an abundant vegetation of Phormidium autumnale.
Mixed with it were small patches of Prasiota crispa which did not
seem to thrive very well where there was plenty of urine, it was
only at some distance from the tank that Prasiola formed vigorous
growths. It is a characteristic fact that no Diatoms were found
among the Phormidium, whereas there were many of them, though
only few species (8 in all), among the Prasiola. Presumably the
Diatoms cannot live in the mucilaginous sheaths of Phormidium
aulumnale, while they evidently thrive well among the íilaments or
leaves of Prasiola crispa. The species most commonly occurring
was Navicula nitrophila.
c. Hlaó (14, 78, 92, 114, 121, 131, 161, 162, 242, 252, 282, 295, 298, 307,
327, 372).
»Hlað« in Iceland means a stretch of ground in front of the
house where there is a constant traffic of people and animals and
where, consequently, planls can only thrive quite close to the house,
and where the »hlað« abuts on the »tún« or homefield, (Jónsson
1900, p. 58). I shall here include under the hlað the trampled areas
at the sides and back of the house as well as a sample froin a
sheep-fold where similar conditions and a similar vegetation are
found. The hlað is always fairly well manured, hence the vegeta-
tion has a nitrophilous character. The predominant alga here is
Prasiola crispa found in 14 of the 16 samples, of rarer occurrence are
Phormidium autumnale (2 samples) and Vaucheria hamata (1 sample).
Diatoms alwajrs occur with tliese, often in a great number of species
and individuals. The characteristic species are Navicula nitrophila,
and N. Atomus. Hantzschia amphioxys, Navicula mutica f. Cohnii,
Diatomella Balfouriana, Pinnularia borealis, and P.parva v. minuta
are also common. P.borealis occurs in nearly all the samples, but
only in a small number of individuals.