30 Morten P. Porsitp. 
to the bottom during the winter. The length of their vegetative period 
especially depends upon the condition of the spring and the autumn. 
In case of a cold spring the ice along the pondshores is rather long 
in melting, and if the autumn sets in early, the ponds are quickly freezing 
up again. During such unfortunate summers the Potamogetonaceae (and 
other waterplants) hardly attain to flowering and not at all to fructi- 
fication, they reproduce by continuous forming of winterbuds. In more 
fortunate seasons the period of vegetation in the same water will last 
long enough for the forming of flowers and fruits. But this is, in our 
area, an exception, all the following species being decided southern 
types with their north limit here. 
As the climatic conditions in the aretic lands vary from year to 
year, and as the amount of warmth necessary to the vital functions 
of the plants is not only relatively, but also absolutely inconsiderable, 
it is no wonder that the same species on the same latitude is sometimes 
found flowering, sometimes quite sterile. 
fi 21. Potamogeton alpinus Bats. 
Itivneq at Holsteinborg 66°58’ (W. & H.), only once collected 
here; the north limit of the species. 
Known from Godthaabfjord and some places in the extreme 
South Greenland. 
At, 22. Potamogeton gramineus L. 
In a small lake near the river to the head of S. Stromfjord ca. 67° (Jens.) 
only once found here. The north limit of the species. 
Elsewhere only known from the southmost part of Greenland 60°—61°. 

Sorensen. The specimens were determined, and of course correctly, by Prof. L. K. 
Rosenvince, but from where it originates. we cannot say. It can not be from 
Rode Ely, this being a cold clacier-torrent in which no phanerogamous water- 
plant is able to thrive, least of all a Potamogeton with a southerly distribution 
as P. gramineus. 
L 23. Potamogeton mucronatus Scurap. (P. Friesii Rupr.). 
Diskofjord in small ponds at Eqalinguit Itivnere 69°32’ (P.) det. Prof. C. 
Raunkrer. Afterwards not seen in Greenland. 
The specimen was sterile. 
a 24. Potamogeton obtusifolius M. & K. 
The district of Egedesminde: Ikamiut inlet in Nivaq Bugt 68°40’ (Kr.). 
The specimens were sterile. 
