Survey of Plant Kingdom 113 



in ice and snow, or in hot springs. Certain species may live symbiotic ally 

 with other organisms for mutual benefits. Algae may live symbiotically 

 with certain fungi in an association known as lichens (li' ken) (Gr. lei- 

 chen, liverwort) , in which case the algae supply foods and the fungi supply 

 water and give protection (Fig. 327). Some species of algae may be 

 parasites, others saprophytes, while a few may be found on other plants 

 as epiphytes (ep'ifite) (Gr. epi, upon, phyton, plant). Certain species 

 of algae will be considered in greater detail in the next chapter. 



C^/orop/ast 



Ce(/ 



.. CeU WqJJ 



QJeocap sa 



Heherocust 



Hormocfon'mm 



Cell 



Qelaiinoas area 



OscUlatona 



spore 



--^XeJI 



Heterocust 



Anah 



ena 



Fig. 29. — Blue-green algae of the phylum Cyanophyta. 



In the following pages each phylum of plants will be considered as to 

 the general characteristics of the phylum as a whole, and a rather brief 

 classification of certain phyla into subphyla, classes, subclasses, with out- 

 standing characteristics, examples, and illustrations, will be given. 



1. Phylura Cyanophyta (si an -of i ta) (Gr. kyanos, blue; phyta, 

 plants). — The blue-green algae are simple, unicellular plants, although 

 certain species may form colonies of similar cells with little differentia- 



