FRESHWATER ALG.E. 147 



form a close felt-like coating at the bottom of almost eveiy ditch. They 

 consist of long, more or less branching filaments, not di\dded into a 

 number of cells, but open from end to end and filled with very dark 

 green endochrome. The cell contents are frequently poui-ed foiiih from 

 the ends of the filaments in the form of large cihated zoospores, of which 

 operation a good description will be found in Hassall's "Freshwater 

 Algae." But there is, in addition to this, a true process of sexual repro- 

 duction, as singular as it is interesting. 



At various points on the filaments are formed two veiy distinct kinds 

 of projections — the first consisting of one or more narrow " horns," as 

 Unger appiopriately terms them, forming short branches from the 

 parent filament, sometimes straight and at others curiously curved ; the 

 second, in close proximity, assuming the form of one, two, or occasionally 

 more, flask-shaped cells, open at their apex. [Plate II., Fig. 8.] In one 

 species, V. raceinosa, both kinds of organ are carried upon a common 

 shaft or pedicel. [Plate II., Fig. 9.] 



The contents of the flask cells gradually assume an irregular 

 spherical shape, wliile those of the " horns " are converted into active 

 Spermatozoids, which issue into the suiTounding water, and thence swarm 

 through the narrow neck of the flask-shaped spore-cells, and there 

 fertihse their contents. These thereafter assume a true spherical form 

 and a distinct cell-covering, while between them and the filaments which 

 bear them dissepiments are formed, at which the heads finally break off, 

 and by decay of their outer walls at length hberate the spores. 



The singular plant Hydrodictyon utriculatum, remarkable for its 

 growth in a network of hexagons, and for the marvellous rapidity of its 

 increase, is referred to the same family (Siphonacece.) A good summai-y 

 of its hfe-history is to be found in the Micrographic Dictionary, and a 

 detailed investigation is recorded in the researches of A. Braun, (Ray 

 Society, 1853.) Some years ago it suddenly appeared in Blackroot Pool, 

 Sutton Park, in enormous quantity; in a few weeks it wholly disappeared, 

 and we have never seen a trace of it since in that habitat. 



The CEdogoniacece comprise two genera, Bulhochcete and GUdogonium ; 

 the former containing only one species, the elegant httle B. setiyent, a 

 plant of great beauty by reason of the long slender bristle-shaped cells 

 wliich form the ends of its lateral branches— a lovely .object, especially 

 by dax'k back-gi-ound illumination. 



It is said to be reproduced by zoospores, and also by a process very 

 similar to that described above as occurring in Vaucheria, each resting- 

 spore being ultimately resolved into foiu- smaller ones, which develop 

 into four new plants. "We have not been fortunate enough to witness 

 these phenomena, although we have frequently gathered the plant, both 

 in our own district and elsewhere. The genus CEdogonium includes 

 several common species, some characterised by a very curious annular 

 structure at the base of many of the cyhndi'ical cells of which the plant 

 is made up, which becomes especially manifest when the filaments break 

 up into separate joints for the emission of zoospores. [Plate II., Fig. 10.] 

 We were once fortunate enough to see this curious process taking place 

 under the microscope in a specimen which had been just mounted, and 



