Mr Marsh, The History of the occurrence of Azolla, etc. 383 
The History of the occurrence of Azolla in the British Isles 
and in Europe generally. By A. S. Marsu, B.A., Trinity 
College. (Communicated by Professor Seward.) 
[Read 9 February 1914.] 
In the middle of October 1913 a species of Azolla was found 
in Jesus Ditch, Cambridge, by Mr H. Jeffreys of St John’s 
College. Mr Moss called my attention to the fact, and at his 
suggestion and with his frequent kind assistance I have identified 
the species and collected a few notes on the distribution of plants 
of this genus in Europe generally and the British Isles in 
particular. 
The Cambridge plant I found to be Azolla filiculoides Lam. 
It was growing among the Lemna, but two or three large patches, 
several metres broad, bore Azolla almost pure, the dull brownish 
colour of the plant as seen in large masses showing up markedly 
against the bright green of the duckweed. When first found 
the plants seemed to be without reproductive organs, but on 
November 2nd it was bearing micro- and macro-sporocarps in 
some quantity. On November 26th, after several sharp frosts, 
the Azolla was growing vigorously, still with sporocarps, and had 
spread over larger areas, at the eastern end of the ditch becoming 
the dominant species of the aquatic vegetation. At the present 
time (February 9th) it is very abundant, but very red in colour 
and broken up into small pieces. 
As to means of introduction of this fern into Cambridge we 
are completely ignorant. The nearest of the previously recorded 
stations is the Norfolk Broads area, while the obvious suggestion, 
that we are dealing with a Botanic Garden escape, is untenable, 
since there was before this discovery no Azolla except A. caroliniana 
being grown at the Cambridge Botanic Garden. 
Azolla, according to Baker*, is a genus with five species 
inhabiting the tropics and warm temperate regions of both hem1- 
spheres. Of these species two have been introduced into Kurope, 
and both occur in the British Isles. These two are A. caroliniana, 
which occurs native in America from Lake Ontario to Brazil, and 
A. filiculoides, from South America. 
The characters of these two species have been well summed 
up in two recent papers on the occurrence of A. filiculoides in 
* Baker, Fern Allies, p. 137, London, 1887. 
+ The distributions are as given in Coste, Flore de France, 1. pp. 702, 703, 
Paris, 1906, and Ascherson u. Graebner, Synopsis der mitteleuropdischen Flora, 
I. p. 114, Leipzig, 1896. 
