TAXONOMY 231 



to more elevated bodies in which the net-like structure of the plas- 

 modium is preserved (plasmodiocarps) to stalked sporangia (spore 

 cases). All of the fructifications, however, produce spores. Dur- 

 ing wet weather amoeboid protoplasts (swarm spores] escape from 

 the spores, each developing a single cilium and moving actively 

 about. In time the cilia disappear and these swarm spores coalesce 

 in smaller then larger groups to form a plasmodium. 



SUBDIVISION III. ALG^ 



Low forms of thallophytes of terrestrial and aquatic distribution 

 consisting for the most part of single cells or rows of single cells 

 joined end to end to form filaments. The higher forms, however, 

 possess structures, which might be compared to stems and leaves of 

 higher plants although more rudimentary in structure. They 

 contain chlorophyll or some other pigment, and so can use the COz 

 and H 2 O in the same manner as higher plants, e.g., in assimilating 

 and providing for their own nutrition. Archegonia are absent in 

 this group. 



CLASS I. CHLOROPHYCE.E, THE GREEN ALG.E 



Green algae are unicellular (sometimes motile), filamentous, 

 colonial, or sheet-like water plants' characterized by the presence of 

 solitary, or numerous chloroplasts in the cells, which compose the 

 thallus. These chloroplasts vary considerably in form, being in 

 some cases spiral bands, in other star-shaped, in others like a napkin 

 ring, and in others granular. In the chloroplasts of most green 

 algae are pyrenoids, which consist of a central crystalline portion 

 of protein (aleurone-like) surrounded by a starchy envelope of 

 variable magnitude. These are called starch centers and the starch 

 is frequently in the form of rounded, or angular grains. The nutri- 

 tion of these algae is autotrophic. There is a definite nucleus present, 

 but in the coenocytic forms the nuclei may be many within the 

 confines of the cell wall. The motile cells have one to many cilia, 

 as likewise some of the reproductive cells. Reproduction is by cell 

 division, the formation of zoospores (motile cells), by zygospores 



