210 THE JOURNAL OF BOTANY 



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. caro- 

 liniana 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 hemi- 

 spheres. Of these species two have been introduced into Europe, 

 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. I 



The characters of these two species have been well summed 

 up in two recent papers on the occurrence of A. filiculoides in 

 Europe, and from the accounts of these authors (viz. Bernard | 

 and Beguinot and Traverso§), from Baker ij and from von 

 Martins, *! the following details of the principal differences 

 between the species are taken. 



Azolla filiciiloides (Lamarck, Encyclopedie Methodique : 

 Botanique, T. i. 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 fiat 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 massulcz or microspore masses have non-septate stalks. The 

 macrospore wall is furnished with large, deep, circular pits. 



Azolla caroliniana (Willdenow, Species Plantarum, v. p. 541, 

 1810). The plants are much smaller with much less dense branch- 



* Baker, Fern Allies, p. 137, London, 1887. 



t The distributions are as given in Coste, Flore de France, iii. pp. 702, 703, 

 Paris, 1906, and Ascherson u. Graebner, Synopsis der initteleuropilischen Flora, 

 i. p. 114, Leipzig, 1896. 



\ Bernard, Recueil des Trav. Bot. Neerland., i. pp. 1-14, 1904, quoted in 

 the Report of the Botanical Exchange Club for 1912, p. 186. 



§ Beguinot e Traverse, " Azolla filiciiloides Lam. nuovo inquilino della 

 flora italiana," Bull. Sac. Bot. Ital., pp. 143-151, 1906. || Baker, loc. cit. 



*'^ von Martius, Flora Branliensis, vol. i. part ii. p. 657, plate 82, Leipzig, 

 1884. 



