502 SUMM.VKY OF CURRENT RESEARCHES RELATING TO 



Grains of Silica and Micrococci of the Atmosphere.* — At the 

 period of the great debate on spontaneous generation between Pasteur 

 and Pouchet, the latter was the first to draw attention to the fact that 

 some of the minute spherical granulations discovered by the Micro- 

 scope in dust deposited from the air in various regions of the globe 

 were essentially composed of silica. That they had often been mis- 

 taken for eggs of Infusoria or for micrococci was very evident, but 

 when the dust was submitted to com[)lete calcination in a platinum 

 crucible the same grains were still visible, with the same forms and 

 dimensions as before. 



Dr. T. L. Phipson has more than once repeated this experiment of 

 Pouchet, but has also made the opposite one, and examined the action 

 of heat upon micrococci, diatoms, and Oscillarias, which are supposed 

 to contain large quantities of silica. There is no doubt but that the 

 dust of the atmosphere reveals to the Microscope, besides the larger 

 mineral fragments, mostly of an angular shape, exceedingly minute 

 circular and spherical bodies, having often not more than 0*001 of 

 a millimetre in diameter, and very similar in size and shape, which 

 resist the action of a white heat in contact with the air and that of 

 strong hydrochloric acid. In some of his observations they were 

 remarkably numerous. Both before and after the action of heat they 

 are more or less transparent. What can be the origin of these 

 singular objects ? The same experiments repeated with siliceous Algte, 

 such as those belonging to the large family of the Diatomaceae, and 

 with tlie micrococci of impure w^aters or vegetable infusions, showed 

 that they do not retain their forms after being subjected to the above 

 treatment, and that in many instances they can be totally destroyed by 

 heat, on the object-glass itself. On the other hand, the fossil diatoms 

 resisted the action of heat and retained their forms. Dr. Phipson can 

 only draw one conclusion from these observations, namely, that the 

 minute siliceous bodies found in the atmosphere are also fossil ; " they 

 are micrococci of another age." 



Lichenes. 



Structure and Development of the Cladonieae.t — E. Wainio in- 

 vestigates this subject from the point of view of the theory of 

 descent. 



With regard to the thallus, the author considers the original form 

 to be horizontal, and consequently that the family should be included 

 rather under the crustaceous than the fruticose lichens. In Cladonia 

 syhatica he was able to follow the development of the podetia (the 

 erect stem-like portions of the thallus which bear the apothecia) from a 

 granular crustaceous thallus ; and in C. uncialis from a scaly layer. 

 The podetium of Cladonia he regards as analogous to the stipes of 

 Bceomyces. The so-called podetium of Stereocaidon has a different 

 origin, and the two genera cannot be regarded as nearly allied. In 



* Cbem. News, xliii. (1881) p. 28. 



t Wainio, E., ' Untersuchung iiber die phylogenetische Entwickelung der 

 Cladonien (in Finnish). Helsin^fors, 1880 (1 pi.). See Bot. Centralbl., ii. (1881) 

 p. 164. 



