Náttúrufræðingurinn - 1956, Page 56

48
N ÁTT Ú RU F RÆÐIN GU RIN N
Description. (Fig. 1 a): Three-lobed, the lobes well separated sticking toget-
her at the base. The middle lobe is 7 tnm long, its
margins running almost parallel up to an obtuse apex.
'l'he lateral lobes, 5 mm long, rise parallel with the
middle lobe, and taper to an obtuse apex. Weak ner-
vation.
(Fig. 1 b): The uppermost part o£ the middle lobe is lacking. The
lateral lobes, measuring 5 mm, branch out somewhat and
taper to a blunt apex. Weak nervation.
The leaves shown in Fig. 2 (a—b) are classified under the Magnoliaceae.
Description. (Fig. 2 a): The leal is 12,5 cm long, greatest widtli near the
middle is 3,8 cm, tapering gradually to the base and
the apex, petiole short, margin entire, midrib stout,
especially the lower part, distinctly striated, 14—16
pairs of secondaries alternating upwards and leaving
the midrib at angles which vary between 45° and 85°.
Towards the margins the secondaries curve upwards
where they fork out forming faint loops. In the
intersecondary spaces the tertiaries form distinct net-
works.
The leaf shown in Fig. 2 1) resembles that mentioned above, being however
somewhat longer (15 cm) and narrower. The difference between these leaves
should not be too great for being explained as a variation. "l'hese leaves should
be compared with the eocene species Magnolia reticulata Chaney & Sanborn
(4). In Fig. 3 a leaf of the living species Magnólía maingayi King is shown for
comparison.
The author has previously published a picture of a leaf from Þórishlíðar-
fjall near Selárdalur, wliich he referred to the genus Fagus. I'he leaf indeed
dosely resembles those from Tertiary plant beds which have been classified
under Fagus. However, after studying Chaney’s and Sanborn’s investigations
of the genus Tetracera in the Goshen Flora (4), I am inclined to believe that
my former conclusion about this leaf may be called in question. Fig. 4 shows
the margin from the middle part of this leaf greatly enlarged. The distance
between the secondaries varies between 4,5 and 7 mm. Most percurrent
tertiaries are closely spaced, greatest distance being only 1 mrn, and appear to
be still closer than they do in the leaves of Fagus.
Pollen-grains occur in great abundance in the plant-bearing strata at Brjáns-
lækur. Formerly the author has mentioned from this locality pollen-grains
of Abies, Cryptomeria, Picea, Pinus and Platanus. Fig. 5 a—d shows a: pollen
grain of Alnus (five-pored, 25,9—29,6 p, abundant), b: pollen-tetrades, (Cf.
Ericaceae, rare), c: pollen-grain similar to those of Taxodiaceae, (37 p, abund-
ant), d: winged pollen-grain showing great resemblance to those of Podocarþus.
Still niore pollen- grains have been determined from the authors collection
among which the following types may be mentioned: lietula-Corylus pollen-
grains, Juglans, Carya, Acer and Ilex.