What is the default Scala version in the maven Scala plugin?

Here's a link to using the maven Scala plugin. But it doesn't mention what exactly the Scala version uses. I created a maven Scala project with the following configuration:

<plugin>
    <groupId>org.scala-tools</groupId>
    <artifactId>maven-scala-plugin</artifactId>
    <executions>
        <execution>
            <goals>
                <goal>compile</goal>
                <goal>testCompile</goal>
            </goals>
        </execution>
    </executions>
</plugin>

      

        
        
        
      

    

Then I create an efficient pom, plugin section for maven Scala plugin:

 <plugin>
     <groupId>org.scala-tools</groupId>
     <artifactId>maven-scala-plugin</artifactId>
     <executions>
       <execution>
         <goals>
           <goal>compile</goal>
           <goal>testCompile</goal>
         </goals>
       </execution>
     </executions>
   </plugin>

      

        
        
        
      

    

And also there is no Scala version in the config tag. So which version of Scala uses the default maven Scala plugin?