217 



NOTE ON THE GEOTROPIC CURVATURE OF THE 



INFLORESGENE IN EICHHORNIA SPECIOSA 



KUNTH (WATER HYACINTH.) 



BY 

 P. S. JlVANNA EAO, 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 observa- 

 tion 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 inflo- 

 rescence I employed the Ganong's auxograph and placing the plant 

 in position connected the tip of the inflorescence with a thread pas- 

 sing 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 interest- 

 ing 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 follow- 

 ing 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. 



