The tissues which develop from apical meristem and procambium are known as primary tissues and these constitute the primary structures of the plant body. The development of the primary tissues causes the stem to grow in length and to some extent in thickness. Stem and root in dicotyledons show secondary growth as they have development of secondary vascular tissues (i.e., secondary xylem and secondary phloem) in them. Flowers, fruits and leaves are primary tissues.