A: The haploid plant body (gametophyte) produces gametes by mitosis
R: Diploid sporophytic plant body produces spores by meiosis

• In alternation of generations, in Bryophytes and Pteridophytes the gametophyte is haploid and produces gametes by mitosis. This is the sexual generation.
  
• When fertilization occurs the gametes join to form a diploid sporophyte. The sporophyte undergoes meiosis to produce haploid spores which will give rise to the gametophyte. This is the asexual generation.
  

So, the correct option is 'Both assertion and reason are correct but reason is not the correct explanation of the Assertion'.