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NOTE ON THE GEOTROPIC CURVATURE OF THE INFLORESCENE IN EICHHORNIA SPECIOSA KUNTH (WATER HYACINTH.)
BY
P. S. JlVANNA RAO, M.A.
,
Agricultural College and Research Institute, Coimbatore.
There are many striking peculiarities about the Water Hyacinth of which the bending of the inflorescence after flowering appears to be very noteworthy. The bending is seen in several stages but observation at definite intervals extending for a few days brings out certain interesting features which are briefly noticed below.
The inflorescence is an elongated erect spike with about 10-15 lilac or mauve coloured flowers arranged at the top of a long shoot. Flowers are medianly zygomorphic conforming to the formula P 3 + 3. A 3 + 3, G (3). There are two sheathing bracteal leaves, inserted one below the other, the lower having a distinct lamina.
The flowers in each inflorescence open simultaneously at about 8 o'clock in the morning, though occasionally a few may lag behind and open on the next day at the same hour.
With a view to ascertain the exact time of bending of the inflorescence I employed the Ganong's auxograph and placing the plant in position connected the tip of the inflorescence with a thread passing round the larger wheel. By tracing the curve on the cylinder which revolves once in an hour I found on the following morning that the curvature actually commences at about 10 in the night. Plants were also kept separately under observation and the interesting fact was noticed viz., that the closing of the flowers and the bending of the inflorescence occur simultaneously at about 10 P.M.
That the curvature is due to geotropism was proved in the following manner. A plant with flowers just open was fitted in a pot which was loosely packed with wet sponge so as to keep the roots moist. The pot was then fixed to the disc of a klinostat and rotated with the plant held horizontally. The roots were further kept moist by being watered at intervals. Though the flowers had closed as usual there was no curvature of the inflorescence even after three days. Hydrotropism does not play any part for the curvature took place when a plant was adjusted with the inflorescence horizontal and completely immersed in water. This shows that the curvature is the result of geotropism only.
