The Botany of Iceland - 01.12.1928, Side 44

368
JOHS. BOYE PETERSEN
of this I mixed with a drop of water on a cover glass, dried it,
and then heated it to red heat on a platinum plate. On the cover
glass I placed a drop of purified styrax dissolved in benzole and
alcohol, the cover glass was slightly heated until the solvents hád
evaporated, and then placed face downwards, on a slide. In this
way I obtained permanent preparations, in which the structure of
the frustules could be closely examined, and where the place of the
individual frustules was practically unchangeable. However, the object
of my investigations was not only to ascertain what Diatom frustules
were to be found in the earth, but in the first place to find out
what species lived on the ground. Hence, after determining tlie
species in the styrax preparation, I had to try and find out from
a preparation in water of the same material what species had ac-
tually lived on the spot, and if, possibly, some of the frustules found
might belong to species that had not lived there at all but had
merely happened to be carried to the place where the sample was
taken. Tliat this might occur we inust be prepared to expect con-
sidering the great resistance of the Diatom frustules. It will be seen,
under the individual species, tliat the samples in which the species
occur are sometimes marked with an L in front of the number.
This is to denote that upon examination of the water preparation
one or more specimens of this species containing »endochrome«
were found in the sample. Since the finer structure of the valve is
not visible in a water preparation, there is a possibility of making
mistakes. However, the probability of such seems to me greatly
diminished by the fact tliat I always beforehand examined a styrax
preparation of the same sample and so knew what species occurred
in the sainple. Moreover, il will not, probably, be possible in such an
examination to see all the species that have lived in the place with
their cell contents, for numerous empty frustules will always be found
in a Diatom vegetation even if it is quite luxuriant. This will perhaps
be the case especially in Diatom growths on the ground where
many specimens will doubtless die in unfavourable (i. e. dry) periods.
As among the Phanerogams, so also among the Diatoms the
species seem very heterogeneous. In some parts of the system,
very small and narrowly delimited species occur, while in other
parts there are more extensive species with numerous varieties and
fornis. This dissimilarity is no doubt in the ntain due to our failing
power to estimate the greater or lesser significance of the systematic
characters employed, hence we are unable to form any decided