THALLOPHYTA 



41 



They are dry, 



are probably the work of the mycelia of a mold-like fungus 

 (Phycomycete) . 



Lichens are thallophytes of wide distribution 

 gray and brown fronds spread- 

 ing over tree trunks and rocks. 

 They represent a union of algae 

 and fungi, since each lichen is 

 actually made up of a fungus 

 and an alga, li\'ing together in the 

 mutually helpful relationship 

 which is called symbiosis. The 

 threads or mycelium of the fun- 

 gus interweave among the cells 

 of the alga, and while the fungus 

 is dependent upon the foods 

 manufactured by the alga, it aids 

 the latter by the protection 

 which its threads afford and by 

 the water which it takes up and 

 holds. 



Fossil lichens have been recognized only from very recent 

 formations. . 



Fig. 10. — • A fungus penetrating an 

 impunctate brachiopod shell on one 

 side only. The round swellings 

 were probably spore sacks. This 

 fungus from the Clinton (Silurian) 

 of Rochester, New York, is proba- 

 bly a member of the Phycomycetes. 

 X 250. (After Loomis.) 



1. What is the source of the energy of plants ? Of animals ? 



2. How do plants eat? Respire? 



3. What difference between the gametophyte and sporophyte 

 phases from algse to seed-plants ? 



4. What significance has this in theories of plant evolution ? 



5. Compare plants and animals (i) as indicators of climate ; 

 (2) as to likelihood of preservation as fossils. 



6. Give the four large divisions of plants with the geologic 

 range and the significance of the name of each. 



7. What distinguishes the thallophytes? 



8. Give distinguishing characters of the five sub-divisions 

 with known geologic range and examples of each. 



9. Upon what is based the division of Algae into green, 

 brown and red groups ? Give examples of each. 



