ZOOLOGY AND BOTANY, MICROSCOPY, ETC. ' 89 



sporangia do not appear to have any resting state. A kind of alter- 

 nation of generation appears thus to be established. 



With regard to the systematic position of this organism, it is 

 doubtful whether the genus Olpidiopsis can be maintained as distinct 

 from CJiy iridium, Cornu's character of the occurrence of a cellule 

 adjacente not being constant. 0. Saprolegnice appears to be parasitic 

 exclusively on Saprolegnia ferax, not being found on Achlya prolifera 

 when the two grow intermixed. 



Organic " Dusts " of the Atmosphere.* — M. E. Yung, of Geneva, 

 lately read a paper to the Helvetic Society of Sciences on organic 

 dust in the atmosphere. With regard to its influence on public 

 health, he distinguishes two groups of particles, the spores of fungi of 

 the mould group, and germs of micro-bacteria, the latter being the 

 more important. In agreement with Miquel's observations f at Mont- 

 souris, he observed a notable increase of germs during the hot months 

 of summer, and a decrease in winter. Opening globes filled with neu- 

 tralized bouillon, quite sterilized by heat, on mountains, glaciers, the 

 ocean, in volcanic craters, and various other circumstances, he found 

 that in most cases ten to twenty cubic centimetres of air sufficed to 

 introduce germs of organisms capable of growing and living in suc- 

 cessive or simultaneous generations, according to species. Two 

 exceptions are noted : one being that of a globe opened at Geneva 

 after an abundant fall of snow ; the bouillon remained quite clear, 

 proving that snow for a time clears the air of germs. The other was 

 that of a globe opened in an isolated ward of the Geneva Hospital, 

 where a diphtheric child was being nursed. On the other hand, fresh 

 snow gathered in winter on the mountains round Geneva, confirmed the 

 previous results as to the extreme diffusion of microscopic organisms. 



M. Yung was unable to prove a connection between the number 

 of atmospheric germs and the recrudescence in the same place of a 

 particular contagious or epidemic disease. 



Green Bacteriaceae and Colourless Phyeochromaceae.J — In con- 

 nection with the well-known existence of certain OscillatoriesB 

 (Beggiatoa and Leptothix) destitute of chlorophyll, and the discovery 

 of Bacteriaceae containing chlorophyll. Van Tieghem rediscusses the 

 relationship of these two families. 



1. Green Bacteriacece. — In the rain-water which filled the cavity of 

 the pileus of a young Polyporus, in the month of September, the 

 author noticed a thin green layer clothing the cavity. This layer was 

 formed entirely of minute rods of a pure green colour, constricted in 

 the middle, dividing frequently and separating after each segmentation, 

 but otherwise immotile. On removing it to ordinary water, there were 

 produced, after a few days, in a large number of these rods, spores of 

 a spherical or slightly oval form, in all respects similar to the well- 

 known spores of Bacillus and other Bacteriaceae. This seemed to 



* Arch. Sci. Phys. et Nat., iv. (1880) pp. 416-8, 573-91 (1 pi.) ; Eugl. Mech., 

 xxxii. (1880) p. 297. 



t See this Journal, iii. (1880) p. 837. 



X Bull. Soc. Bot. France, xsvii. (1880) pp. 174-9. 



