578 



SCIENCE. 



[N. S. Vol. Xn. No. 303. 



gram of the latter occupied the sessions on 

 Thursday. A symposium on the plant geog- 

 raphy of North America had been arranged 

 for Friday, June 29th, in which the follow- 

 ing papers were read : 



' Distribution of the Spermatophytes in New Eng- 

 land ' : B. L. Robinson. 



' Distribution of tbe Spermatophyta in Southeastern 

 United States ' : J. K. Small. 



' Notes on the Lower Austral Element in the Flora of 

 the southern Appalachian region ' : Thos. Keaknby. 



' Physiographic Ecology of Northern Michigan ' : H. 



C. COWLKS. 



' Vegetative Elements of the Sandhill region ' : Eos- 

 coE Pound. 



' Composition of the Rocky Mountain Flora ' : Pee 

 Axel Rydbeeg. 



'Flora of the Columbian Lavas ': C. V. Pipee. 



' Distribution of the Grasses of North America ' : G. 

 V. Nash. 



' Relationship between the North and South Amer- 

 ican Floras ' : W. L. Beay. 



' Floral Zones of Mexico ' : J. N. Rose. 



' Origin of the flora of North America ' : N. L. Beit- 

 ton. 



The committee on bibliography reported 

 that the publication of the card catalogue of 

 literature relating to American Botanj^ had 

 been undertaken by the Torrey Botanical 

 Club. 



The Bacterial Air-Flora of the Semi-Desert Re- 

 gion of Neiv Mexico : By John Wbinzirl. 

 The study of the air-flora of our semi- 

 desert region possesses considerable in- 

 terest, especially since no similar investi- 

 gation has been made under the same 

 conditions. Oar climate is characterized 

 by extreme dryness, intense sunlight, hot 

 summers and mild winters, and possesses 

 considerable altitude.* Outside of the 

 river valleys and in the mountain ranges, 

 vegetation is scarce. Because of these 

 facts it is generally supposed that practi- 

 cally no bacterial life exists here. In mak- 

 ing this investigation, it was thought that 

 simple petri plate exposures would give re- 



*The altitude of Albuquerque is nearly 5,000 feet. 



suits sufl&ciently accurate for our purpose. 

 Later a number of quantitative determina- 

 tions were also made, a sand filter and 

 aspirator can being used for this purpose. 

 Eegulation petri plates of approximately 

 3.5 inches internal diameter were used. 

 Agar-agar seemed to be the most suitable 

 medium, since the high colors of the air 

 germs are especially prominent upon it. 

 For comparative purposes, the number of 

 bacteria falling upon the plates were re- 

 duced to a basis of 10 min. exposures. The 

 number of plates exposed at one time was 

 usually three, the results being averaged 

 for the final figure. Seventeen exposures 

 were made near the University of New 

 Mexico, which is situated upon an elevated 

 table land or ' mesa ' east of Albuquerque. 

 The time covered seven months — Septem- 

 ber to May. The number of bacteria fall- 

 ing upon the plates during 10 minutes was 

 35.8. The number fell as low as 3.8 in 

 February, and rose to 71 in September. 

 Thus the falling off in number during the 

 winter season was quite marked. Com- 

 parative experiments were also made be- 

 tween the air of the ' mesa ' and that of the 

 residence and business districts of Albu- 

 querque, the population of which is about 

 10,000. For approximate ratios we have 

 1:6 between mesa and residence district; 

 and 1:80 between mesa and business dis- 

 trict. Similar experiments were made to 

 show the difference between the air in the 

 morning and evening for residence and 

 business parts of the city. For the former 

 we have an approximate ratio of 1:4 ; and 

 for the latter 1:5. It need scarcely be 

 added that the great increase for the 

 evening (6 P. M.) is due to the activities 

 incident to city life. A special test of 

 the altitude factor was made in the latter 

 part of July, 1900, the Sandia Mfes. be- 

 ing selected for the experiments. Plates 

 were exposed in the usual way, at approx- 

 imately 7,000 ft,, 8,500 fb. and 10,000 ft., 



