340 Mr. J. Ralfs on the Nostochinese. 



Aphanizomenon agrees in its filament with Oscillaturia, but is 

 sufficiently separated by its conspicuous sporangia, which are si- 

 milar to those of Dolichospermum. It differs from all the other 

 genera in the Nostochinece by the absence of vesicular cells and by 

 its obsoletely articulated filament. 



1 . A. Flos-aquce (Linn.) . Filaments cohering laterally in flat lamellae 

 which separate at their extremities into fasciculi ; sporangia cylin- 

 drical with an inconspicuous covering. Byssus farinacea virescens, 

 aqucB inspersa, Linnaeus, Flora Lapponica, no. 532 (1737), ed. 2nd, 

 p. 388 (Smith, 1792) ; Flora Suecica, ed. 1st, no. 1128. Byssus 

 Flos-aquce, Linn. Species Plantarum, no. 1168 (1753), ed. 2nd, 

 p. 1637. Conferva Flos-aquce, Roth, Catalecta Botanica, fasc. 3. 

 p. 192 (1806). Oscillatoria Flos-aquce, Agardh, Synopsis Alga- 

 rum Scandinavian, p. 107 (1817) ; Syst. Algarum, p. 59. Nostoc 

 Flos-aquce, Jiirgens, Algae aquaticae. Limnanthe Linncei, Kiitzing 

 in Linnaea, vol. xvii. p. 86. Limnochlide Flos-aquce, Kiitzing, 

 PhycologiaGeneralis, p. 203 (1843) ; Phycologia Germanica, p. 168; 

 Species Algarum, p. 286 ; Tabulae Phycologicae, t. 9 1 . fig. 2 a. Apha- 

 nizomenon incurvum, Allman in lit. cum specimine. 



Probably not uncommon. Grand Canal Docks, Dublin, Professor 

 Allman. 



Sweden, Linnceus ; Germany, Kiitzing. 



I am indebted to Professor Allman for a beautiful and cha- 

 racteristic specimen of this species. In its dried state the stra- 

 tum appears to be composed of minute flocculi, and, with the 

 exception of colour, might not unaptly be compared to scattered 

 snow-flakes. The colour is opake, seruginous green, which how- 

 ever becomes more or less altered after being dried a second 

 time. The microscope shows that the flocculi consist of parallel 

 filaments united together laterally, and forming a flat layer which 

 appears plumose from the filaments converging at the ends into 

 little conical or subulate tufts or pencils. The filaments are 

 straight, obtuse, not attenuated ; the joints are rather longer than 

 broad, faintly visible, and especially difficult of detection in con- 

 sequence of their granular contents. Kiitzing describes the spo- 

 rangia as elliptic. In the Dublin specimen they are few in number 

 and immature; but in specimens given me by Professor Kiitzing 

 they are linear, much elongated, often ten or twelve times longer 

 than broad, and resemble those of the next species except in 

 having a far less conspicuous hyaline covering. The best di- 

 stinctive mark between these species is the lateral coherence of 

 the filaments in A. Flos-aquce. 



In the dried state, the only condition in which I have seen it, 

 the Aphanizomenon Flos-aquce is easily recognized by its floccu- 

 lent appearance, even to the naked eye. I believe that not only 

 was it one of the earliest-known plants in this group, but that it 



