The plant body of bryophytes lacks the true roots, stem or leaves. It grows prostrate on the ground and is attached to the substratum by delicate, unbranched, unicellular hair like organs called the rhizoids. The bryophytes like the thallophytes lack the vascular tissue (xylem and phloem) characteristic of the higher plants. All bryophytes exhibit alternation of generation but it is always of heterologous type (i.e. sporophytes and gametophytes are of different types). Gametophytes of bryophyte are green, leafy individual and due to presence of chlorophyll they are autotrophic in nature the sporophyte is dependent for its nutrient wholly or partially on the gametophyte plant to which it is attached organically throughout its life.