The Flora of Lake Tanganyika. 
249 
THE FLORA OF LAKE TANGANYIKA. 
T the Linnean Society on December 20th Dr. Rendle and Mr. 
A G. S. West gave some account of the botanical results of the 
Third Tanganyika Expedition, conducted by Mr. Cunnington in 1905-6. 
It will be remembered that as a result of his two expeditions to 
the great Central African lake, Mr. J. E. S. Moore came to the 
conclusion that its peculiar fauna showed distinct traces of marine 
origin, and put forward the hypothesis that the lake had been isolated 
from the sea in Jurassic times and had ever since retained a portion 
of the marine fauna which it possessed in that epoch. Imaginative 
botanists thereupon dreamed dreams of freshwater Brown and Red 
Seaweeds inhabiting the lake and presenting all sorts of unexpected 
possibilities in algal evolution. 
Mr. Cunnington’s extensive collections of the flora of the lake 
do not however support this theory. The account which Dr. Rendle 
gave of the aquatic flowering plants showed that for the most part 
they are widely distributed tropical types, and in many cases are 
found also in Nyassa and Victoria Nyanza. Furthermore of those 
which were found in Tanganyika alone, nearly all are known from 
other parts of the w r orld and certainly do not suggest a marine origin. 
Of these Nnias marina , for instance, in spite of its name, is found not 
only in the Norfolk Broads and the Norwegian fiords but also in the 
Swiss lakes. The cosmopolitan Potamogeton pectinatus and the very 
common tropical yussicea repens are other examples. 
When we turn to the Algae the case is not much stronger. Mr. 
Cunnington made a very large collection of the plankton both from 
Nyassa and Tanganyika, and in addition to a number of cosmopolitan 
forms such as Pediastrwn, Botryococcus, Melosira, Steplianodiscus, 
Anabeena fos-aquce, some more restricted type, such as the diatom 
Surirella Nyassensis, and Chodatella subsalsa a minute green plankton- 
form with long bristles, hitherto known from the shores of the Baltic, 
were found. Also a new tubular alga, constricted at intervals, w hich 
is to be called Sphinctosiplion. Out of the w'hole number of plankton 
algae found in Tanganyika a very large percentage are certainly 
peculiar to it, but it cannot be said that the case for the marine 
origin of its algal flora has been in any w r ay made out. 
Mr. Cunnington said that Tanganyika, shut off from communi¬ 
cation with other waters, with a high rate of evaporation and a 
small drainage area, had evidently for a long time been decreasing 
in volume and probably increasing in salinity. The older travel¬ 
lers always said its w f ater tasted peculiar. Then apparently a time 
came when it was suddenly filled up by waters from the 
north, and the lake also acquired an outlet to the Congo basin. 
Now again its level is evidently lowering again, for it is easy to see 
traces of the lake many feet above its present level. 
Thus it may well be that the fauna and flora have had to adapt 
themselves to increasing salinity, and the long period of isolation 
which the lake has evidently undergone has, no donbt, had a 
differentiating effect on the inhabitants. This would account for 
the large number of endemic species of animals and plants. Of a 
specifically marine origin Mr. Cunnington’s botanical results, 
at least, seem to furnish no evidence. 
