The Botany of Iceland - 01.12.1928, Blaðsíða 4

INTRODUCTION.
In a previous paper on the aérial algæ of Denmark (1915, p. 273)
I defined the concept »aérophilous algæ«. The defmition an-
swered fairly well to its purpose of delimiting a definite biological
group of algæ in Denmark. However, it had certain drawbacks,
and evidently did not cover conditions in other countries quite so
well. Puymaly has furthermore taken exception to the term itself
and suggests the designation »aériens« for these algæ. I agree with
him, and in this work I shall employ the term »aérial algæ«, thereby
further indicating tliat the delimitation of the biological group here
dealt with is not the same as that employed by me in 1915. In
the firsl place I here include the Cyanophyceæ whether or not
they form resting spores, and also several Chlorophyceæ which
may likewise form special resting stages under unfavourable con-
ditions. It has turned out tlrat several of the algæ included by me
under the true aérophilous algæ in 1915 (e. g. Zygogonium ericeiorum
(West and Starkey 1915, Fritsch 1916), Hormidium flaccidum
(Piercy 1917)) may, in fact, pass into more or less pronounced
resting stages and so survive unfavourable periods. Many other
green algæ (e. g. Apatococcus lobatus, Botrydiopsis arhiza) may deposit
a considerable amount of fat and other reserve food-stuffs in dry
periods, and pass into a resting stage without the cell being es-
sentially altered. It is then difficult to draw the line between what
must be regarded as ordinary vegetative cells and resting cells, hence
I will not here attempt to distinguish between algæ with resting
stages and the other algæ. Whether or not the Diatoms are capable
of forming resting stages we do not know. The so-called craticular
forms, which have from olden limes been observed in various
Diatoms (Eunotia, Achnanthes, Melosira Dickiei, Navicula, Surirella),
have, particularly by Pfitzer (1871, p. 103 f.), been regarded as a
kind of resting stage, a means by which the species survives un-
favourable conditions. More recently craticular forms have been