AZOLLA IN BRITAIN AND IN EUROPE 211 



ing. They lie flat on the surface of the water. The roots are 

 not as numerous or as conspicuous as in A. filiculoicles. The 

 margin of the upper leaf lobe is not as broad as in the other 

 species, and the trichomes of the upper surface are said to be 

 bicellular, though I have not been able to observe this character 

 satisfactorily. The glochidia have 3-5 transverse septa in the 

 stalk, and the macrospore wall is not pitted but merely finely 

 granulate. 



The history of the genus in Europe began in 1872, when 

 A. caroliniana was introduced into Continental botanic gardens, 

 whence it soon escaped into neighbouring ditches and ponds, and 

 multiplied enormously. In 1878 De Bary described it as a " new 

 water- pest " in Kassel, and in 1885 it was very abundant at 

 Leyden and Boskoop in Holland. * It was also found at Bonn, 

 Giessen t and Strassburg ^ in 1885, and in Berlin in 1887.]: In 

 Bohemia it was found by Celakovsky near Pilsen in 1895, and it 

 had spread much earlier into England (1883), France (1879), and 

 Italy (1886). § 



In England A. caroliniana was first obtained at Pindon 

 (Middlesex), and an account of this is published in Science Gossip 

 for 1883. It has been recently reported from various spots in the 

 Thames valley, between Oxford and London, but it must be 

 remembered that until Ostenfeld ji pointed out the fact in 1912 

 (from specimens found in 1911) it was not realised that we had 

 any Azolla other than A. caroliniana. For instance, DrucelT 

 (1908) gives only one species, A. caroliniana. The following 

 records for the British Isles have been published, though, until 

 the material has been re-examined in the light of Ostenfeld's 

 discovery, they must be considered recoi'ds for the genus rather 

 than for the species. Azolla described as A. caroliniana has been 

 found at Hayes Place (Kent), Oxford, Sonning, Henley, Enfield, 

 Sunbury and Suleham.*" Of these I have been able to examine 

 material from Sunbury and Enfield kindly sent by Mr. 0. E. 

 Britton. The Sunbury plant is ^. filiculoicles, the Enfield specimen 

 A. caroliniana. Another Azolla from Enfield was sent by Mr. 

 HoUoway, but this was A. filiculoides. The Norfolk Azolla, which 

 is good A. filiculoicles, has also been several times referred to as 

 A. caroliniana. I have seen A. caroliniana from one other British 

 locality, viz. Godalming, where it was found in 1913. 



The species is described by Ascherson and Graebner (1896) 



* Kittel, Gartenfiora, 1885. 



t Dosch u. Scriiia, Excursionsjlora Hessen, 3te Auflage, p. 24. 

 I Luersseii, Farnpflanzen, p. 598. 



§ This account is taken chiefly from Ascherson and Graebner, loc. cit., 

 but see also Saccardo, Cronologia della Flora I(aZ/(i;!rt, Padova, 1909 ; Ibid., 

 " De diffusione Azollie earoliuianffi per Europam," Hedwigia, 1892, p. 217; 

 Beguinot and Traverso, loc. cit., where many additional references are given. 



Ij Ostenfeld, " Floristic Eesults of the International Excursion," New Phyt. 

 xi. p. 127, 1912. 



H Druce, List of British Plants, p. 88, Oxford, 1908. 



♦* Reports of the Botanical Exchange Club, 1910, p. 609; 1911, p. 56 ; 1912, 

 pp. 186, 220; Journal of Botany, xl. p. 113, 1902; xlviii. p. 332, 1910. 



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