#2   In pea plants, which stem length (long or short) is dominant?

          In each case of the big graphic, the dominant form of the allele is presented first
          and the recessive second.  That's the only way you could have known this
          answer.  Long stem just happens to be dominant.  It is not because it is long.
          It just is!   In some other species, short stems are dominant.  Nobody knows
          why!  Making assumptions on which is dominant or recessive are just that  --
          assumptions.  Sometimes you're correct and sometimes you're wrong.