Simple Plants With Chlorophyll — Algae 151 



7. Thallophytes usually live in water, or moist places, and do not 

 possess rigid tissues for extensive upright growth. 



8. Many species of thallophytes, both algae and fungi, are of great 

 economic importance, both beneficially and detrimentally. 



GENERAL CHARACTERISTICS OF ALGAE 



The term algae does not apply to a natural group of plants, but it is 

 a desirable name applied to those thallophytes which carry on photo- 

 synthesis because of the presence of chlorophyll. The algae vary greatly 

 among themselves, and many of them resemble certain fungi in many re- 

 spects. There are several characteristics which are common to both 

 algae and fungi, except that the former possess chlorophyll, while the 

 latter do not. These facts will be discussed in this chapter and the next. 



Algae are common in fresh water and in the salt waters of the oceans 

 (marine) . They may be free living in fresh or salt water, where, together 

 with the animals, they make up the so-called plankton (plangk' ton) (Gr. 

 plangktos, wandering). Others may live on the bottom, where together 

 with the animals, they constitute the so-called benthon (ben'thon) (Gr. 

 benthos, depths of the sea). Certain species may grow in moist soils, on 

 moist rocks and trees, in snow and ice, or in hot springs. Certain species 

 may live symbiotically with other organisms for mutual benefits. Algae 

 may live symbiotically with certain fungi in an association known as 

 lichens (li'ken) (Gr. leichen, liverwort), in which case the algae supply 

 foods and the fungi supply water and give protection. Some species may 

 grow on other plants as epiphytes and on animals and may be saprophytes 

 or parasites. 



BLUE-GREEN ALGAE (PHYLUM CYANOPHYTA) 



These are simple, unicellular plants although certain species may form 

 colonies of similar cells among which there is little differentiation. In 

 addition to the green chlorophyll, there is a blue pigment called phyco- 

 cyanin (fi ko -si' anin) (Gr. phykos, alga or seaweed; kyanos, blue). 

 Sometimes a red pigment may also be present in certain species. The 

 chlorophyll is distributed throughout the cell and not localized in definite 

 bodies known as plastids (Fig. 29). There is no definite, organized nu- 

 cleus; the nuclear, chromatin materials are scattered throughout the cen- 

 ter of the cell. The cells are often surrounded by a slimy, gelatinous 

 sheath. Because of this, myxophyta (myx-of'ita) (Gr. myxo, slime; 



