While walking along roadside, Sunil asked his father, a biology teacher, whether some small, green, non-flowering, leafy and thalloid plants, having little differentiation of body and growing along pavement are of any use to us. Father answered that these plants are small but they play very important role in maintaining green cover on the land. (i) To which group these small thalloid, green, non-flowering plants belong? (ii) In what way bryophytes are useful to us? (iii)Which other groups of plants act as colonizers of barren rocks and make land suitable for growth of higher plants? Do these plants play some role in pollution monitoring?