What does it print? I'd guess from looking that it prints the line
"..toString.."; this is what you might call a "side effect" of the function
call: it returns the empty String after all that work, but the first
statement in the method is a console print statement. What do you expect?

The toString() method is expected to return a String, so what is it good
for that it only returns an empty String??
( return ""; )

And why are you running through all your LifeForms in your Vector,
create a String from them and then do nothing with it??

Instead you could easily write

public class VectorOfLifeForms {
   public String toString() {
      return VECTOR_OF_LIFE_FORMS.toString();
   }
}

Because the toString() method of Vector (or rather of it's super class
AbstractCollection) does all you want for you - iterates over all it's
elements, calls their toString() method and returns a String composed
the String representations of all your life forms.

(By the way, your Vector is named strangely - only constants which
cannot be changed should be named in uppercase. For a Vector that
doesn't make much sense...)

Now try in your main method

System.out.println(myVectorOfLifeForms.toString());
//                 ^- or however your instance of VECTOR_OF_LIFE_FORMS
//                    is named

Greetings,
Stefan