Page:The Journal of Indian Botany, Volume III.djvu/215

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Two species of Monochoria, M. hastaefolia Presl., and If.

Linn., were studied with reference to the floral dimorphism as an adaptation for cross-pollination by insects. These species are plants commonly found on the banks of streams and in marshes all over India. They have blue trimerous flowers consisting of six perianth lobes, six stamens, (five being small, yellow and sterile, the posterior fertile stamen being large and blue, with its filament spurred on one or both sides), and a three-celled superior ovary with a style and a minutely six-fid stigma, (Fig. 3). The flowers are aggregated in terminal inflorescences (symposial cymose pseu-do-racemes) which are centripetal in the smaller species, M. vaginalis, and centrifugal in the more robust M. hastaefolia, { plate I).

The flowers of both the species of Monochoria show an interest- ing form of dimorphism produced as a result of the bending of the fertile posterior stamen to one side, either to the right or to the left, and a corresponding bending in the opposite direction of the style. Thus two types of flowers are seen, (1) those in which the stamen bends to the right and the style to the left and (2) those in which the bending is reversed, (Plate II and Figs. 4 and 5.) Flowers of both types occur in the same inflorescence. But it has also been noticed that flowers opening on any one day on an inflorescence were mostly of one type.

The anthers of the posterior fertile stamen dehisce through terminal slits which may later on extend downwards ; the tips of the anther and the stigma are at the same level on either side of the flowers. The importance of this dimorphism is as an adaptation for cross-pollination by insect visitors. If an insect visits the flower the anther-tip and the stigma touch the right and left parts of the body and if the insect were to visit the same type of flower no polli- nation could be effected. But if it were to visit the other type of flower where the positions of the anther and the stigma are reversed* it effects cross-pollination as that part of the body originally smeared