Decbmbeb 31, 1920] 



SCIENCE 



641 



is probable tbat the gas collected from the 

 fusion or high-temperature treatment would 

 require no further purification for therapeu- 

 tic use. 



The liberation of small quantities of emana- 

 tion by high temperatures has already been 

 successfully applied in the quantitative meas- 

 urement of radium by the emanation method. 

 There is nothing novel in the idea, and its 

 application has already been tested out under 

 somewhat different conditions. The object of 

 the present note is simply to call attemtion 

 to the possibility of applying the same prin- 

 ciple to the collection of large quantities of 

 emanation for therapeutic use, and to leave 

 the field open for experimentation by the 

 different laboratories and companies inter- 

 ested. 



The procedure might be varied in several 

 ways. Fusion might be employed with or 

 without a flux; possibly temperatures con- 

 siderably below fusion will be found to liber- 

 ate emanation from some salts with a satis- 

 factory recovery. The salts come mainly in 

 consideration are: The chloride, bromide, car- 

 bonate and sulfate. "With the chloride or 

 bromide the corresponding lithium salt might 

 prove to be a good flux. Experiments with 

 other salts of radium might disclose one that 

 would yield its emanation at a still lower 

 temperature. 



It should also be investigated whether the 

 state of fusion per se is favorable to the 

 liberation of emanation. It is possible that 

 a viscous fusion just above its melting-point 

 would not liberate emanation so readily as 

 the more porus salt before fusion. The effect 

 of various proportions of barium should also 

 be studied, as well as volatilization losses 

 under various conditions with different salts. 



The heating should preferably be electrical, 

 but whether internally or extemaly applied 

 is a matter for determination. 



The collection after liberation might be by 

 means of mercury displacement or by liquid 

 air condensation. 



S. C. LlND 



Golden, Colorado, 

 November, 1920 



A QUANTITATIVE SURVEY OF THE FLORA OF 

 LAKE MENDOTA 



In the summer of 1919, quantitative deter- 

 minations were undertaken for the Wisconsin 

 Geological and Natural History Survey, of 

 the submerged vegetation of Lake Mendota, 

 Madison, "Wis. The object of the work was to 

 form an estimate of the total amounts of the 

 various species present in the lake, and to 

 obtain such additional data as might be avail- 

 able on their comparative distribution. 



The plants were gathered by hand from 

 measured areas of the lake bottom. For this 

 purpose the whole plant zone of the lake was 

 divided into stations according to local differ- 

 ences in physical and floral characteristics. 

 Samples were gathered at different depths in 

 each station. The plant zone is continuous 

 around the lake in water not deeper than 7 m. 

 The samples thus gathered were separated 

 into their component species, and their wet 

 and dry weights determined. 



For purposes of calculation the plant zone 

 was divided into three depth-zones, namely, 

 to 1 m., 1 m. to 3 m., 3 m. to 7 m., this 

 arbitrary classification being based on evi- 

 dent differences in the character of the vege- 

 tation at different depths. By averaging 

 the weights of the various samples gathered 

 within one depth-zone, and comparing this 

 average with the total area of that zone, as 

 measured on a map, the total weight of each 

 species in each zone was computed, and by 

 addition the total weights for the whole plant 

 zone. 



The total amount of plants collected in this 

 way was some 93 kilograms wet, 11 kilograms 

 dry, the average water content being about 

 88 per cent. This material was obtained in 

 221 samples taken from 35 stations. The 

 yield of the entire lake, estimated on the 

 basis of these collections, is in round numbers 

 18,500,000 kilograms wet, 2,100,000 kilograms 

 dry. The total area of the plant zone is 

 10,040,000 square meters. The yield per unit 

 area is therefore 18,426 kilograms per hectare 

 wet, 2,091 kiligrams per hectare dry (or 16,215 

 pounds per acre wet, 1,840 pounds per acre 

 dry). 



