has reported on the remarkable variation in morphology of an organism, a member of the green sulfur bacteria, which he designated as Chlorobiutm limicola. According to van Niel, his organism occurred as coccoid forms, as long rod to club-shaped cells, and as loosely or closely wound spirals; also, in his cultures, the spherical and ellipsoidal shapes appeared to be common. Pringsheim (Bact. Revs., 13, 47-98, 1949) in commenting upon the variability of van Niel's Chlorobium says, "This polymorphism surpasses that of every other microorganism and should be confirmed...." Skuja (Symb. Botan. Upsaliensis, 9, 3, 1948) has indicated that his cultures of C. limicola contained only the streptococcus form and occurred in a range of size from 0.3 to 0.5 ,u in diameter. Bocher (Det. Kgl. Danske Videnskabernes Selskab. Biologiske Meddelelser, Bind XXI, no. 1, 1949), reporting upon the flora of the lake Flynderso, hesitatingly assigned his green bacteria to the genus Pelogloea. He indicated that the green bacteria in the Flynderso belonged mainly to the rod type but that round forms and streptococci did develop. He indicated further that the rodshaped organisms were 0.5 to 0.7 ,u in width and, on the average, from 0.2 to 0.5 A in length. Other green bacteria which reminded him of C. limicola and which were dominantly rod shaped were 0.7 to 0.8 ,u in breadth. In connection with a bacteriological survey' on the ecology, distribution, and nutrition of the aquatic bacteria of Sodon Lake, we have had occasion to study the exact morphology of a bacterium designated by us as C. limicola Nadson. This organism has been reported on by Bicknell (Lloydia, 12, 183, 1949) and Newcombe (Ecol. Monographs, 20, 207, 1950). Our organism was isolated by the single cell isolation technique and also by the use of enrichment cultures. Studies of the absorption spectra indicate the presence of the bacterio-viridin peak of Metzner (Ber. deut. botan. Ges., 40, 125, 1922). Electronographs2 (figure 1) show, for the most part, typical cocci; however, there is a range in length of 1.0 ,u to 1.25 ,u and 0.75 ,u to 1.0 , in width. These measurements have been determined by reference to particles of polystyrene latex. The average size of the organisms under consideration is approximately 0.75 IA by 1.0 ,u. The extremes in pleomorphism as observed by van Niel are not evident in preparations made from cultures started from single cells.
