Rice fields are water-logged for several months, promoting an abundant growth of algae. Algae exercise multiple beneficial effects on the crop . The beneficial effect of algae on the rice crop is ascribed mainly to fixation of atmospheric nitrogen by blue-green algae . DE (1939), SINGH (1942SINGH ( , 1961)), WATANABE (1949WATANABE ( , 1956WATANABE ( , 1959WATANABE ( , 1962)), FOGG (1956), DE & SULAIMAN (1950), SUBRAHMANYAN, RELWANI & MANNA (1964) and others have studied in some details the fixation of nitrogen by Cyanophyceae and its effect on the growth and yield of rice plants . In addition to the nitrogen fixing Myxophyceae the rice fields support a large number of other algae, which do not fix atmospheric nitrogen, and which both quantitatively and qualitatively outweigh the nitrogen fixing algae .
There is evidence for the presence of growth hormones in many algae (KNIGHT, 1947 ; BURROWS, 1956 ; WEBER, 1958 ; THIMAN et al ., 1942 ; WILLIAMS, 1949 and BENTLEY, 1958) . But their effect on the growth of crop plants has not been investigated . GUPTA (1964) observed, that Scytonema hofmanni, Fischrella mucicola and Nostoc sp . cannot only grow in the absence of combined nitrogen but that rice seeds pretreated with their extracts germinate much earlier than the normal untreated seeds . Recent observations by GUPTA & KusuM LATA (1964) on paddy seeds pretreated with the extracts of Phormidium spp . which do not fix atmospheric nitrogen show that seed germination is markedly accelerated. In view of the, above, observations have been made in detail on the effect of presoa-