The Botany of Iceland - 01.12.1928, Síða 29

THE AERIAL ALGÆ OF ICELAND 353
in the island and found that it varies from 4.8 (mýri) to 7.6 (running
water). Thus very acid soil does not seem to occur, nor very basic
soil either.
Next to the moisture of the soil, the factor of greatest impor-
tance to the algæ growing on the surface and having no organs
that can penetrate the earth, is no doubt its content of food-stuffs,
especially manures. I shall be able to underlake an approximate
classification based on this factor with the aid of my notes, whereas
a classification according to the degree of moisture would require
observations of tlie individual localities through protracted periods.
There is a number of samples which it has been impossible to
classify according to more general viewpoints. For these I refer
the reader to the preceding list of the samples examined.
In the following I shall first deal with habitats where manures
are present in greater or less amount, taking first the localities wliere
they are found in the greatest quantities. Next I shall mention
various natural formations where manures are not found in any
noticeable amount.
The soil in Iceland is in general very moist owing to the fre-
quent rains. The localities mentioned in the following under a-e
have all abt. the same amount of moisture. The surface itself, where
the algæ grow, may apparently become quite dry in dry weather,
but lower down tliere will always be found some moisture which
will prevent the desiccation at the surface having any great effect.
The homefield as a rule slopes downward from the farm, in its
upper part it is therefore as dry as the »hlað«, but in its lower
part it is often considerably moister. »Mvri« is land where the
ground-water slands so high that the surface is always moist, hence
it is doubtful whether the algæ growing there may be included
among the aérial algæ. The algæ on »flói« where tlie ground-water
just reaches the surface or comes a little above it, I consider hydro-
philous, and so do not deal witli them in the present work.
a. Soil Fertilised by the Droppings of Birds. (Samples 209, 212).
On the small island of Geitey near the eastern shore af Mývatn,
under the dense growths of Archangelica, I found the ground covered
with a thick layer of bird’s droppings, a regular guano deposit, ori-
ginating from the numerous aquatic birds that had their haunts
under the plants. The only alga found here was Phormidium