LOWER PLANTS 



151 



Stem, and root-like structures; some even have an 

 erect axis with whorls of branches from top to bottom 

 or only at the top; structures display some tendency 

 toward cellular differentiation but no tissues are 

 present (Figure 9.1). 



Cells: distinct or without cell walls so nuclei are 

 in a continuous cytoplasm; nucleus complete and 

 complex, one to many per cell; cytoplasmic pigments 

 normally in grass-green plastids; one or more large 

 central vacuoles; cell wall mostly two layers, the inner 

 firm, mostly cellulose layer and the outer gelatinous 

 layer; certain stages generally with flagellae. 



.\utntion: mostly photosynthetic. 



Reproduction: asexual by mitosis (unicellular spe- 

 cies), fragmentation (colonial and filamentous types), 

 and spore production; some species form spores simi- 

 lar to those of the Cyanophyta; others also form 

 mobile, flagellate spores in a cell modified as a spore- 

 producing structure (sporangium); in a very few cases 

 gametes develop without first being fertilized; sexual 

 involves diplobiontic and both haplobiontic life cy- 

 cles; life cycles either are of both gametophyte and 

 sporophyte being single-celled or multicellular, or are 

 of one generation being suppressed to a phase and the 

 other being "the plant"; diplobiontic cycles have both 

 generations of the same or different form and in- 

 dependent plants or one generation growing upon the 

 other; gametes are of the same form or different form 

 with distinct eggs and sperms. 



Occurrence: approximately 90 per cent fresh water 

 and 10 per cent marine; most marine forms are inter- 

 tidal and attached to rocks; most fresh-water species 

 are submerged; also in moist land habitats and upon 

 other algae, plants, and animals; some saprophytes, 

 parasites, and lichen formers; about 6500 species. 



CHAROPHYTA (Stoneworts) 



Structure: multicellular and macroscopic, greenish 

 plants consisting of simple root-like "hairs"; of an 

 erect, stem-like, branching axis; and of branches 

 (often leaf-like) arranged in whorls at interrupted 

 points on the axis; structure and pattern of develop- 

 ment from a single cell is suggestive of horsetails; 

 plant often heavily covered with calcium carbonate, 

 origin of their common name; some cellular differen- 

 tiation, but no true tissues; sex organs are present 

 (Figure 9.2). 



Cells: distinct, complete and complex with cell 

 walls; structure much as in Chlorophyta; flagellae 

 absent except in sperm. 



asymmetrical 

 colony 



thick filaments 





€}%■■■ "^^ 



^.„!« 



^^.."^^"tt^ft ,#^ 



sph^^^e ^,,r^;m 



forked tubular 



tubular crust 



Figure 9.1 Green algae types, about natural size, but the flat mem- 

 brane, thick filament, and forked tubulor types often are much larger. 



