Page:The Journal of Indian Botany.djvu/257

219

General : — Bladders in plants are comparatively rare and where fchey occur, they are of doubtful significance in most cases. The best known instances where such structures are conspicuously seen are Sargassum, Fucus, Nercocyslis among the Fucaceae, Trapa (Onagracea?) species of Utricularia, and Eichhornia speciosa (Pontederiacea?). Except in Utricularia where the bladder has been definitely proved to be an insect-catching and insect-preying organ, the functions of the bladders have been generally supposed to be either to serve as floatative or swimming organs or to serve as air reservoirs. In most of the above examples the ecological value has been better known rather than the physiological cause, and the present investiga- tion was undertaken purely from the latter point of view. It applies only to Eichhornia speciosa, a study of which was made in the Botanical Laboratory at the Agricultural College and Research Institute, Coimbatore, where the weed attracted notice in connection with the proposed legislation for eradicating it in certain parts of the Madras Presidency.

Though Eichhornia is a water plant it thrives in such a variety of situations that observers have differed regarding its exact habitat. Kerner (7) for instance, states that the plants are not fixed in the mud beneath the water by roots but float freely on the surface of the pond. He further characterises Eichhornia as a swimming plant distinguishing it from floating plants like Trapa which are held fast to the muddy bottom beneath by means of roots. Schonland (10) on the other hand describes it more correctly as either swimming entirely and free on the water or rooting in shallow water in mud, the leaf stalks in the former case becoming strongly swollen and functioning as swimming bladders. Without seriously contradicting these authors it may be stated that plants with and without bladders are found in deep water the determining factor for bladder formation being, as will be seen below, not the depth but a plentiful supply of water that is physiologically available. The plant is also not restricted to any particular surrounding but is at home in ponds, tanks, old wells, ditches, in marshy areas and in fact in any stagnant