384 Mr Marsh, The History of the occurrence of Azolla 
Europe, and from the accounts of these authors (viz. Bernard* and | 
Béguinot and Traverso+), from Baker{ and from von Martius§, 
the following details of the principal differences between the 
species are taken. 5 | 
Azolla _filiculoides (Lamarck, Encyclopédie Méthodique: 
ae 
Botanique, T. 1. p. 343 and plate 863, 1783). The plants are 
in dense tufted masses, the ends of the shoots being porrect and 
often protruding, not lying flat on the surface of the water as in . 
the other species. The whole shoot is much larger and thicker, 
the branching is more compound and the branches are closer ° 
together. The upper lobes of the leaves have a broad distinct | 
margin and bear numerous unicellular trichomes on their upper ° 
surfaces. The reproductive organs show the most distinctive © 
characters. The glochidia or hooked hairs which are attached to 
the massule or microspore masses have non-septate stalks. The » 
macrospore wall is furnished with large, deep, circular pits. 
Azolla caroliniana (Willdenow, Species Plantarum, V. p. 5441, 
1810). The plants are much smaller with much less dense branch- 
ing. They lie flat on the surface of the water. The roots are 
not aS numerous or as conspicuous as in A. filiculoides. 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 {] 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) tf. . 
* Bernard, Recueil des Trav. Bot. Néerland., 1. pp. 1—14, 1904, quoted in the 
Report of the Botanical Exchange Club for 1912, p. 186. 
+ Béguinot e Traverso, ‘‘Azolla filiculoides Lam. nuovo inquilino della flora 
italiana,” Bull. Soc. Bot. Ital., pp. 143—151, 1906. + Baker, loc. cit. 
§ von Martius, Flora Brasiliensis, vol. 1. part 1. p. 657, plate 82, Leipzig, 1884. 
|| Kittel, Gartenflora, 1885. 
{| Dosch u. Scriba, Excursionsflora Hessen, 3° Auflage, p. 24. 
** Luerssen, Farnpflanzen, p. 598. 
++ This account is taken chiefly from Ascherson and Graebner, loc. cit., but see 
also Saccardo, Cronologia della Flora Italiana, Padova, 1909; Ibid., ‘De diffusione 
Azolle caroliniane per Europam,” Hedwigia, 1892, p. 217; Béguinot and Traverso, 
loc. cit., where many additional references are given. 
