New aspects in the ontogeny of carpels in Michelia champaca Linn

Abstract

The carpel primordium comprises the midrib and marginal meristems. Activity in the marginal meristems results in the formation of short projections towards the adaxial side of the primordium. These projections represent the incipient laminal halves. Subsequently, rapid abaxial growth in the carpel leads to the displacement of the marginal meristems in an involute direction. Thus, the marginal meristems move closer and the abaxial tissues get adpressed due to involute growth. Another interesting result of rapid abaxial growth is the appearance of tissue projections (abaxial appendages) from the adpressed abaxial part. The abaxial appendages exhibit false margins but do not possess mariginal meristems, the component cells being highly vacuolated and enlarged. The loculus is formed by the expansion of the ventral surface lying between the marginal meristems which by this time transform into placental surfaces. At this stage the carpel can be resolved into midrib, loculus, incurved marginal placentae and adpressed abaxial appendages whose primary function appears to be development of stigmatic papillae at the terminal regions of the carpel. It is possible that the various types of simple carpels in the Ranales have diverged because of the different lengths their abaxial appendages have attained.