The Botany of Iceland - 01.12.1928, Qupperneq 66
390
JOHS. BOYE PETERSEN
Originally these diflerent forms were described as varieties or even
as distinct species, but Cleve reduces them all to formæ. (Syn. I, p. 129).
Transition forms occur between various of the forms but I am not sure
whether it is the case with all of them. The systematic rank of these
forms can probably only be established by culture experiments. For
ecological purposes it seems to me convenient to keep them distinct for
the present. Whether we call them species, varieties, or forms is of no
great consequence. As I have had fairly good material under observa-
tion of this species, I shall here attempt to give a general view of its
various forms as far as my observafions go.
A. Valve without undulated edges
I. Valve perfectly symmetrical, elongate-elliptic, slightly
produced rounded apices, striation closer at apices
than in middle......................................... f. Wtdffii.
II. Valve + asymmetrical
/\ Valve shorter or longer linear
1. Apices protractæ............................... f. producta.
2. — capitatæ................................ í. ventricosa.
/\ /\ Valve elliptic-lanceolate
* Length more than 13 p,
a. Apices produced, obtuse . . . ............. f. Cohnii
b. Apices not produced
1. Valve lanceolate, abt. 3 times as long as
broad, apices acute..................... f. Göppertiana.
2. Valve lanceolate, swollen in middle,
apices obtuse........................... f. rhomboidea.
3. Valve abt. twice as long as broad, apices
rounded, distinct apical area........... f. elliptica.
** Length less than 13 p......................... f. minima.
f. undulata.
f. Peguana.
f. Legumen.
B. Valve with undulated edges.............................. f. quinquenodis.
(nivalis?)
f. binodis Hust.
f. rhombica.
Of the forms with undulated valve edges I have only observed
f. quinquenodis. I cannot therefore speak of them from personal inspec-
tion, nor can I say anything about the forms described by Playfair (1914,
p. 112), viz. v. ovalis, v. subhexagona, v. subcircularis.
NB. Forms showing a coarse structure like that of N. m. Cohnii
were observed in some samples from Vestmannaeyjar. They approach
N. muticopsis West. I have seen no pronounced f. Göppertiana (V. Heurck
Syn. Pl. X, flg. 18, 18b, Van Heurck, Types No. 114) in Iceland, but