CONFERVOIDEvE HETEROGAM.E. 119 



is in touch with that characteristic of the Floridese, the 

 highest order of Algse. 



The simplest type, illustrated by a somewhat rare alga, 

 Sphceroplea annulina, consists of an unbranched filament 

 of superposed cells, having very thick, perforated, trans- 

 verse septa ; the plant is moncecious, that is, having both 

 sexes produced in different parts of the same individual. 

 Asexual reproduction is unknown. Certain of the cells of 

 a filament become oogonia, others antheridia; the contents 

 of the former break up into several oospheres, each having 

 a colourless " receptive spot," at which fertilization by the 

 absorption of an antherozoid takes place. The contents 

 of the antheridia change to a dull red colour, and break up 

 into a large number of biciliated zoospores, which pass into 

 the oogonia through the perforations in the transverse septa. 

 The fertilized oospheres become clothed with a thick, warted 

 cell-wall, and change to an orange-red colour. The mature 

 oospheres remain within the parent filament during the 

 resting-stage, and frequently float on the surface of the water 

 for some time during the autumn, as a thick, orange-red felt. 



In the spring the resting-spores on germination produce 

 three or four zoospores, each of which changes into a fusi- 

 form or spindle-shaped cell, with thin hair-like ends : from 

 this cell the plant grows by cell-division. 



In the genus CEdogoniuin, the sexual mode of reproduction 

 is more complex than in Sphaeroplaea, and the mode of 

 cell-formation is of a very peculiar type, not met with else- 

 where in the Vegetable Kingdom. 



Several species are common in fresh-water streams and 

 ponds, and all agree in consisting of an unbranched single 

 row of cells, containing clear green protoplasm, and by the 

 presence of a considerable number of rings, or striae, close 



