X. ECOLOGY 



Simplest Plant Body a Thallus. — It has been found by botanists 

 that the plants which are the simplest in body structure are those 

 which live in the water. Sometimes such simple plants are found 

 upon rocks or on the bark of trees. In such plants we can dis- 

 tinguish no root, stem, or leaf. 



^^ The plant body may even be 



^^^^ ^1^ spherical in outline and con- 



^^^^L^ ^^P!^k ®^^^ ^^ ^^^' ^ s^^g^^ ^^^^- Such 



^^^mb||^J|^ ' ^B^^^ ^^6 the plants which give the 

 ^^^^9^9 fi^^^^^^ green color often found on 

 ^^^JUTJ^^^ >^be bark of trees. Still other 



•^^jnP^B^ plants are threadlike in ap- 



pearance. Others, as sea- 



A red seaweed, an example of a thallus body. i i_ -i i t_ i 



weeds, have a ribbon-shaped 

 body. All of these diverse shapes of plant bod}^ are grouped 

 under the general name of thallus. The simjplest jorms of plants 

 have a thaUuslike body. 



Adaptation to Environment. — This kind of body is of use to 

 a plant which lives in the water as a root to take in water. Plants, 

 as well as animals, are greatly affected by what immediately sur- 

 rounds them, their environment. It is believed (and we have 

 shown in our experiments) that the environment (conditions of 

 temperature, moisture, soil, etc.) is capable of changing or modify- 

 ing the structure of plants very greatly. The change ivhich a 

 plant or animal has undergone, that fits it for conditions in which it 

 lives, is called adaptation to environment. 



The factors which act on plants and which make up their environ- 

 ment are soil, water, temperature, and light. 



The first plants were probably water-loving forms. It seems 

 likely that, as more land appeared on the earth's surface, plants 

 became adapted- to changed conditions of life on dry land, 



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