The Marine Diatoms of the Canadian Arctic Expedition, 
1913-18 
By ALBERT Mann 
Diatomist, Carnegie Institution, Washington, D.C. 
The following report is a rather fragmentary contribution to the marine 
diatom flora of the Arctic seas. The number of gatherings secured was small 
and the different species they contained turned out to be comparatively few. 
The list therefore compares poorly with what would have been obtained from 
the richer floras of other parts of the world. This is not at all a surprising fact, 
for previous studies of Arctic diatom material have shown that in diversity of 
species it is uniformly very scanty. As to why this is so no satisfactory explan- 
ation has been found. One is disposed to assume that the rigorous temperatures 
and the long winter nights of these high latitudes must affect the diatoms as 
they are known to do some other organisms, checking a tendency to elaborate- 
ness of structure and consequently to that variability which would after a 
while give us those differences on which we depend for the separation of species. 
And in fact we do find that the Arctic diatoms as a class are surprisingly simple 
in form and much less elaborate in their ornamentation than those of other 
regions. Especially is there a preponderance of the so-called Naviculoid diatoms, 
rather plain, boat-shaped structures, with simple designs of ornamentation, 
and destitute of those horns, arms, spines, etc., that often adorn the species 
growing in warmer waters. So that, if we were to draw deductions from the 
evident and unusual simplicity of the diatoms of all Arctic gatherings, including 
those here recorded, we would be pretty sure to infer that cold and darkness 
had here brought into existence a flora singularly suppressed in its ornamenta- 
tion. 
But a study of the diatoms of the Antarctic seas forbids our putting too 
much stress on this inhibition of low temperature and darkness. Without 
denying wholly its influence, we find in the Antarctic, where equally frigid 
waters and long periods of night occur, one of the most varied:and elaborately 
ornamented diatom floras now living. There the cruder and perhaps more 
primitive Naviculoid group is in the decided minority, round polygonal and 
other symmetrical shapes being more common, and usually adorned with com- 
plex sculpturing and a variety of horns, spines and other ornamental append- 
ages. If therefore frigid temperatures and long winter nights are responsible 
for the simplicity in structure and poverty of species of the Arctic: diatoms our 
theory only conjures up another equally difficult problem, namely, why these 
same factors fail to operate in the Antarctic region. Consequently, as above 
stated, a good explanation of the marked simplicity of Arctic diatoms is not 
known to the writer. 
There is, however, one fact, perhaps too inconsequent to merit serious 
thought, which it may be worth while to mention: the Antarctic differs greatly 
from the Arctic in its approaches. The latter region is joined to the vast seas 
that flow around the world by only two comparatively narrow channels, a 
condition due to the fact that both the Eastern and the Western hemisphere 
have their broad areas at the extreme north and taper away to a point south- 
ward; so that the shores of North America on the west are close to those of 
Asia and on the east to those of Europe; and furthermore, the chief ingress 
current into the Arctic in through the narrower of these two openings, namely, 
3697—1} 3Fr 
