58 .CONFERVOIPEJ:. 



smaller (E), and originate singly (in the species figured) in small 

 conical cells (c, d in A\ The oogonia are developed at the 

 extremities of certain branches : they are bottle-shaped cells with 

 very long and thin necks (trichogyne), open at the end (a in A); 

 at the base of each oogonium is a spherical oosphere. The sper- 

 matozoids reach the oosphere through the trichogyne, or through 

 an aperture in the wall when the trichogyne is absent, and fertili- 

 sation having taken place, the oogonium becomes surrounded by a 

 cell-layer (envelope), which grows out from the cells near its base 

 (b in A), and in this way a kind of fruit is formed (B) (spermocarp, 



cystocarp) . 



The oospore, next spring, divides and forms a parenchymatous 

 tissue (homologous with the Moss-sporophyte) ; this bursts open 

 the envelope (C), and a zoospore (homologous with the spores of 

 the Moss-capsule) arises in each of the cells, and produces a new 

 Goleochcete. We have then, in this case, a still more distinct 

 alternation of generations than in GEdogonium. Only one genus, 

 Coleochcete, is known, but it contains several species, all living in 

 fresh water. 



Order 8. Cladophoraceae. This order is probably derived 



from the Ulothricacea?. The thallus consists of a single, un- 



branched or branched filament, generally with an apical cell. 



The cells have each 2 or more nuclei. Asexual reproduction by 



zoospores with 2 or 4 cilia, and by akinetes. Conjugation of 



gametes with 2 cilia is found in some genera. They occur in salt 



as well as in fresh water. The principal genera are: Urospora, 



Chcetomorpha, Ithizoclonium, Cladophora; of the last named genus 



the species C. lanosa and C. rupestris are common in salt water ; 



C. fracta and C. glomerata in fresh water. 



Order 9. Gomontiace*. Gomontia polyrrhiza, the only species hitherto 

 known, is found on old calcareous shells of certain salt water Molluscs. 



Order 10. Sphceropleaceae. The thallus consists of free, un- 

 branched filaments, with very elongated multinuclear cells. The 

 ve-etative cells form no zoospores. Sexual reproduction by 

 oogamous fertilisation (see page 13, Fig. 10 B). The oospore has 

 a thick wall (Fig. 10 D) studded with warts, and assumes a 

 colour resembling red lead. It germinates only in the following 

 spring, and produces 1-8 zoospores, each with 2 cilia (Fig. 10 E), 

 which grow into new filaments. Only one species, Sphceroplea 

 unnulina, is known. 



