54 CONFERVOIDE5). 



1, 2, or 4 cilia), akinetes or aplanospores ; tlie last named may 

 germinate immediately, or only after a period of rest. Sexual re- 

 production takes place by the conjugation of gametes of about the 

 same size, each having two cilia (Fig. 52 d). The zygote of 

 Ulothrix, on germination, produces a brood of zoospores which 

 swarm for a time and then elongate to become t/7o/m'#-filaments 

 (alternation of generations). The gametes may also germinate 

 without conjugation in the same manner as the zoospores. The 

 principal genera are : Ulothrix, Hormidium, Conferva, Micro- 

 spora. Ulothrix zonata is very common in running fresh water. 

 Nearly all the species of Hormidium occur on damp soil, tree- 

 stems and stones. 



Order 3. Chsetophoraceae. The thallus consists of a single, 

 branched, erect or creeping filament of cells, often surrounded by 

 mucilage. The cells have only one nucleus. Asexual reproduc- 

 tion by zoospores with 2 or 4 cilia, by akinetes, or aplanospores., 

 In many, conjugation between gametes with 2 cilia may be found. 

 They approach on one side, Ulothricaceae, and on the other, My- 

 coideaceae. The principal genera are : Stigeoclonium, Draparnaldia, 

 Chwtophora, Entoderma, Aphanochcete, Herposteiron, Phceothamnion, 

 Ohlorotyliuin, Trichophilus, Gongrosira, Trentepohlia. Most of the 

 species of Trentepohlia are coloured red by the presence of a red 

 colouring material, which occurs in addition to the chlorophyll. 

 They are aerial Algse which live on stones (T. jolithus, "violet 

 stone," so named on account of its violet-like odour in rainy 

 weather), on bark and old wood (T. umbrwa), or on damp rocks 

 (T. aurea}. Trichophilus welckeri lives in the hair of Bradypus. 



Order 4. Mycoideaceae. The thallus is discoid, consisting of one or more 

 cell-layers, and is always attached. Asexual reproduction by zoospores with 2 

 or 4 cilia. Sexual reproduction in some species by the conjugation of gametes 

 with 2 cilia. This order forms the connecting link between CJicctophoraceae 

 and Coleochcetacea. The species occur in fresh water (Chtetopeltis) as well as 

 in salt (Pringsheimia), on the carapace of tortoises (Dermatophyton=Epiclem- 

 niydia), or endophytic between the cuticle and the epidermal cells of the 

 leaves of tropical plants, destroying the leaf-tissue (Mycoidea). 



Order 5. Cylindrocapsaceae. The thallus consists of a 

 simple (rarely, in parts, formed of many rows) unbranched 

 filament, attached in the young condition, which has short cells 

 with a. single nucleus, and is enveloped in a thick envelope with 

 a laminated structure. Asexual reproduction by zoospores with 

 2 cilia, which are formed 1, 2, or 4 in each vegetative cell. The 



