DIFFERENT TYPES OF OVULE AND ITS CHARACTERISTIC

Types of Ovules
               
                        We have now seen different types of ovules on the basis of nucellar features. But

ovules in the angiosperms exhibit diversity with respect to their size, degree of ovule

curvature, nucellus thickness, integument number and thickness, formation of

micropyle, funiculus length, degree of vasculature etc. The most commonly used

classification of ovules is based on their orientation and curvature. There are mainly

six types of ovules:

    Orthotropous or Atropous ovule

           i) The body of the ovule is straight and errect.

             ii) The chalaza and the micropyle remain in one line.

            iii)  It is considered as the most primitive ovule.

            iv) It is very common in gymnosperms and in angiosperms it is seen in

                  Polygonaceae, Piperaceae and Urticaceae.

   Anatropous ovule

          i) The ovule is inverted here so that the micropyle faces downwards and lies

                 closeto the hilum

            ii)  It is yery common in angiosperms and is designated as the typical

                 apgiospermic ovule.

            iii)  The outer integument is fused with the funiculus on one side making the

                   raphe

    

  Amphitropous ovule 

          i) in this type the curvature of the ovule is very pronounced.

             ii) The micropyle is very dose to the funicle and remains at the side of the

                 funicle facing laterally downwards.

            iii) The embryo sac is horse shoe like or transversely oriented.

            iv) Such ovule types are seen in Allismaceae, Butomaceae

Campyotropous ovule

         i) It is a gurved ovule and the ovule is bend so that the micropyle comes close

                to funicle.

           ii) But the chalaza and micropyle donot lie in the same line.

           iii) It is sen in members of Leguminosae, Capparidaceae, Chenopodiaceae.

 Hemianatropous ovule or Hemitropous 

             i)The body of the ovule is at a transverse position and makes a right angle to

                the funiculus.

             ii) The micropyle and the basal halaza remain in one line and parallel to the

                 surface.

             iii) It is seen in Ranunculus, members of Primulaceae, Malpighiaceae.

Circinotropous ovule 

              i) It is a much coiled ovule

              ii) the funicle grows so much that the upright facing ovule faces down wards

                  and again turns upwards like the anatropous type

              iii) There is a 360 tum of the ovule due to funicular growth.

              iv) It is seen in members of Cactaceae e.g. Opuntia and some members of

                 Plumbaginaceae.

types of different ovule in angiosperms