HOW TO KNOW THE FRESH-WATER ALGAE 



Figure 158 



224a Cells cylindrical, usually many times their diameter in length 



(sometimes only 3 times longer than wide); wall thick. Fig. 158. 



RHIZOCLONIUM 



Fig. 158. Rhizoclonium Hookeri Kuetz. 



The species belonging to this genus are all 

 coarse, wiry, and but very little (if at all) 

 branched. The filaments are composed of rela- 

 tively long, cylindrical cells with thick walls 

 which frequently show lamellations, especially 

 near the cross walls. There are numerous 

 chloroplasts, often compactly arranged and dif- 

 ficult of determination in respect to shape and 

 organization. There are many pyrenoids. The 

 branches are usually short and mostly at right 

 angles to the main axis, but when they are long 

 these plants intergrade with some forms of 

 Cladophora (Fig. 192), in which the branching 

 habit has been reduced. Rhizoclonium forms 

 dense, tangled filamentous mats in standing 

 water, or long, stringy, sometimes rope-like 

 strands in flowing water. R. hieroglyphicum (Ag.) Kuetz. is the most 

 common species, one which has rather uniformly cylindrical cells with 

 relatively thin walls, and does not branch. 



224b Cells not cylindrical, slightly larger at the anterior end, or even 

 when appearing cylindrical always with at least 1 ring-like scar 



at the anterior end just below the cross wall. Fig. 159 



OEDOGONIUM 



Fig. 159. a, Gedogonium crispum Kuetz., por- 

 tion of filament with one fertilized and an un- 

 fertilized egg; b, basal hold-fast cell and por- 

 tion of a filament containing antheridia and 

 antherozoids; c, Oe. Westii Tiffany, showing 

 dwarf male filaments epiphytic on the female 

 plant. 



There are over 250 species in this large genus 

 which belongs to a family (Oedogoniaceae) in 

 which there are only two other genera (Bulbo- 

 chaete, Fig. 195; Oedocladium, Fig. 174). Spe- 

 cies are differentiated by the size and morpholo- 

 gy of the sexual reproductive organs and by the 

 shape, decoration, and size of the mature zygo- 

 spore (oospore). Whereas some species have 

 the male organs (antheridia) in filaments the 

 same size as the female, others possess dwarf 

 male plants that grow as epiphytes on or near 



Figure 159 



102 



