In the cultivation of rice the algæ of the paddy field have been found to be of extreme importance. Brizi in Italy has shown that although rice is grown under swamp conditions yet the roots of the rice plant are typical of those of ordinary terrestrial plants and have none of the structural adaptations to aquatic life so characteristic of ordinary marsh plants. Hence the plants are entirely dependent for healthy growth upon an adequate supply of oxygen to their roots from the medium in which they are growing. A serious disease of the rice plant, characterised by the browning and dying off of the leaves, which was thought at first to be due to the attacks of fungi, was found to be the effect of the inadequate aeration of the roots, while the entry of the fungi was shown to be subsequent to the appearance of the physiological disease. The presence of algæ in the swamp water was found to prevent the appearance of this disease, in that they unite with other organisms to form a more or less continuous stratum over the surface of the ground, and add to the gases which accumulate there large quantities of oxygen evolved during photosynthesis. The concentration of dissolved oxygen in the water percolating through the soil is thereby raised to a maximum, and the healthy growth of the crop ensured. This work has been corroborated by Harrison and Aiyer in India, and a sufficient supply of algæ in the swamp water is now regarded as one of the essentials for the production of a good rice crop. From what has been said, it appears that, although our knowledge of the soil algæ is extremely limited, and our conception of the part they play is largely based on speculation, yet the subject is one of enormous interest and worthy of investigation in many directions. In its present undeveloped state, it is a little difficult to foresee which lines of study are likely to prove most profitable, but there is little doubt that eventually the soil algæ will be shown to play a significant part in the economy of the soil. SELECTED BIBLIOGRAPHY. * _Papers giving extensive bibliographies._ I. GENERAL. [1] Bristol, B. M., “On the Retention of Vitality by Algæ from Old Stored Soils,” New Phyt., 1919, xviii., Nos. 3 and 4. [2] Bristol, B. M., “On the Alga-Flora of some Desiccated English Soils: an Important Factor in Soil Biology,” Annals of Botany, 1920, vol. xxxiv., No. 133. [3] Brizi, U., “Ricerche sulla Malattia del Riso detta ‘Brusone,’ Sect. IV. Influenza che le alghe verdi esercitano in risaia,” Annuario dell Instituzione Agraria Dott. A. Ponti, Milan, 1905, vol. vi., pp. 84-89. [4] Esmarch, F., “Beitrag zur Cyanophyceen-Flora unserer Kolonien,” Jahrb. der Hamburgischen wissensch. Anstalten, 1910, xxviii., 3. Beiheft, S. 62-82. [5] Esmarch, F., “Untersuchungen über die Verbreitung der Cyanophyceen auf und in verschiedenen Boden,” Hedwigia, 1914, Band lv., Heft 4-5.