266 ALG.E. 



division and most of them also by a kind of sexual repro- 

 duction, in which the contents of two distinct individual 

 cells become commingled, and the resulting mass finally 

 resolves itself into a number of new individual cells or 

 plants. 



Forms of a higher grade of structure are represented 

 by the fine hair-like filaments which we find floating in 

 rivulets, water-troughs, and ponds, rooted at one extremity 

 to stones or to larger water-plants. Many of these 

 filamentous species (Confervoidece) multiply themselves 

 asexually by the protoplasmic concents of the cells, which 

 applied end to end in a single row form their filaments, 

 becoming resolved into innumerable minute bodies, called 

 zoospores, motile by means of the lashing of exserted 

 very delicate protplasmic threads (cilia), which break out 

 of the cells and rush about in the water until they finally 

 settle down, acquire a cellulose membrane, and so lose 

 their motility and grow. 



The same species generally present also a sexual pro- 

 cess of reproduction, varying in complexity from the 

 simplest condition, in which two accidentally contiguous, 

 but precisely similar, cells of the same or different fila- 

 ments mingle their contents and so form a germ-spore, 

 giving origin to one or more individuals, to conditions 

 presenting considerable diversity between the sexual cells, 

 more especially manifest in the male-cell (antheridium\ 

 which when diverse in form from the female-cell (pogo- 

 nium) usually liberates motile zoospore-like antherozoids, 

 which become merged in the contents of the oogonium 

 and so determine the development, either immediately 

 or after a pause, of a germ-spore. 



The yet more complex species, such as the Olive- 

 coloured Sea-weeds (Fttci), which clothe the rocks 

 between tide-marks upon our shores, possess a compli- 

 cated reproductive system of spores and antheridia, 

 contained in minute cavities (conceptacles), each opening 

 outwards by a pore, at the thickened extremities of the 

 divided fronds. Their mode of reproduction, which is 

 only sexual, adapted to the medium in which the 

 species grow, agrees in essentials with that which is 

 characteristic of Ferns and Mosses ; with this difference, 

 however, that the coatless germ-cells are actually set 



