The Botany of Iceland - 01.12.1928, Side 43

THE AERIAL ALGÆ OF ICELAND
367
here enumerate the species found, but refer the reader to Ihe pre-
ceding lists (p. 343). This association of Diatoms does not seem to
show any special characteristics; it consists of a mixture of the usual
terrestrial and hydrophilous species. Altogether I do not think that
specially therinophilous Diatom species occur.
4. Temporary Algal Associations.
By »Formations passagéres« Comére (1913, p. 5) means algal
associations living in puddles, ditches, and similar places wliere the
amount of water is so small that it entirely disappears in the dry
summer time. The algæ growing in such places can hardly be in-
cluded among the aérial algæ, since they are quite submerged during
growth. When the water evaporates, some of them will be able to
form resting stages that will survive desiccation, others die away
with the exception of a few individuals that have found shelter
below other algæ which protect them against evaporation, others
again perhaps die out entirely. The vegetation in these places will
therefore be variable, and you cannot count on finding the same
species in the same waterhole each year. What species develop
will depend upon which species survive the preceding period of
desiccation, and what germs have happened to be added in the
moist period. Hence it cannot be expected that the few samples
I have collected from this kind of localities in Iceland should give
a complete picture of this algal association. I shall not, therefore,
attempt to describe the characteristics of the algal ílora but refer
the reader to the lists of species in the preceding summary of the
individual localities. The samples of »formations passagéres« are
133, 140, 302.
SYSTEMATIC ENUMERATION OF THE SPECIES
OBSERVED.
CYANOPHYCEÆ
(SEE THE PRECEDING PAPER).
DIATOMACEÆ.
The Diatoms live principally in the top layer of the earth or
among the mosses and algæ on the ground. 1 therefore scraped
the uppermost thin layer off the samples of earth collected. A little