2 So THE BEGINNINGS OF LIFE. 



spores of fungi are much smaller, but very many of them 

 are quite large enough to be appreciable wherever they 

 really occur. According to Pineau, those of Pemcillium 

 glaucum vary from -3-^" to -^-j^' in diameter, and 

 M. Pasteur himself gives the dimensions of the spores 

 of the most common species of the genus Ascopkora 

 as from TT Vir" to WoV ^ n diameter. All such spores 

 or ova should therefore be almost as easily recognizable 

 as particles of starch. But whilst the latter are encoun- 

 tered with the greatest frequency, the former are only 

 very rarely found. 



In the same year, it occurred to M. Pouchet and also, 

 quite independently, to MM. Joly and Musset 1 , that 

 the examination of snow flakes would be a very good 

 means of obtaining some knowledge as to the nature of 

 the particles existing in the atmosphere. Their anti- 

 cipations were fully verified. The large snow flakes did 

 entangle the atmospheric particles, so that especially 

 during the commencement of a snow storm they were 

 found to contain a very large quantity of almost all 

 the ordinary varieties of atmospheric particles and 

 fragments: and these differed in nature according to 

 the localities in which the snow fell. But, in addition, 

 M. Pouchet says 2 : c This snow contained a consi- 

 derable number of Protococcus pluvialis, of a beautiful 

 green colour.' Rain, collected in a suitable vessel as 

 it fell, has also been examined by Mr. James Samuelson, 

 who was one of the earliest of those who paid attention 



1 Compt. Rend.' 1860, 1. 1. p. 647. 2 ' Nouv. Exp<5r.' p. 76. 



