74 OF THE FILAMENTOUS ALGJE. 



than is the case with the greener and more compact portions 

 of the tuft. Specimens of the conjugating filaments should 

 always be obtained, if possible, as the characters of several 

 of the genera are based upon this curious phenomenon. I 

 may mention among others Mougeotia, Mesocarpus, Pleuro- 

 carpus, Craterospermum, Staurospermum, Ehynconema, and 

 Spirogyra. In all these the sterile filaments are of little 

 service in affording generic characters, whereas (except 

 in the one mentioned last) the presence of conjugating 

 examples marks the genera at once, even after they are 

 dried. 



Another remarkable phenomenon, the so-called ' Swarm- 

 ing Spores,'* common to all the filamentous Alga?, is most 

 easily observed in the species of Ulothrix. The escape of 

 the Zoospores from the parent cell generally takes place in 

 the early part of the day, and betrays itself even to the 

 naked eye by a green film which forms on the water's 

 edge when the Algas are kept in a glass vessel. It may be 

 observed, too, in the (Edogoniaceaa, especially in (Edogo- 

 nium fonticola, in which the swarming spores may be seen 

 at almost any period of the year. The cilia with which 

 these spores are furnished defy detection on account of the 

 almost incredible swiftness of their movements ; but they 

 may be seen easily enough if a drop of solution of iodine f 

 be allowed to work its way by capillary attraction under 

 the covering glass. As the solution mixes with the. water, 

 it paralyses and finally kills every object of an organic 

 nature with which it comes in contact. While this is 

 taking place, the observer must keep his eye fixed upon the 

 dying spores, applying a rather oblique — at any rate not 

 too bright — illumination, and then he will see the glistening 

 threads as they swing to and fro. 



Many of the Cladophorge, Confervas, and GEdogonise, 



* It takes its name from a fancied similarity of the movements of 

 the Zoospores in the parent cells to the swarming of bees. — Ed. 



f Either iodine dissolved in alcohol, or an aqueous solution of 

 iodide of potassium. 



