136 W. ARCHBR. 



spores commenced germinating and the algae remained in a 

 living condition, but the formation of mould upon the slides 

 was not kept down. 



2. By carrying on the culture in a space su2:)plied Avith 

 air, previously purified by passing through a plug of cotton 

 wool. In this way I anticipated that I shoxdd get rid of 

 mould ; it was further probable that the continuous access of 

 fresh air would operate favorably. 



The apparatus which I employed consisted of a horizontally 

 placed lamp-chimney, connected at one end with an aspi- 

 rator ; two slides covered with spores and algae were intro- 

 duced into it, and under the slides there was a stratum of 

 water, intended to maintain the moisture of the air ; the 

 chimney was then closed at the other end with a perforated 

 cork, wherein fitted a glass tube, twice bent, and at the end 

 blown out into a globe, open at one end and filled with 

 cotton wool. 



I could not expect that in this way fungal spores would 

 he absolutely excluded from my cultures, because Pasteur 

 found that air passed through one cotton plug still leaves 

 germs upon a second one. Since, however, the tube through 

 which the air passed was further bent in two places, there 

 was a good chance that fungal-spores, which were carried 

 by the air through the wadding would not arrive at the 

 cultures. 



An experiment with this apparatus (from October 1st to 

 November 3rd, 1872) showed me, indeed, that it was well 

 adapted for the purpose ; still it taught me afresh how little 

 certainty one has in the success of experiments in the culture 

 of lichen-spores ; on both the slides, though the algae had 

 remained in a good condition, the spores had sent out no ger- 

 minating filaments, and this notwithstanding that there were 

 present no apparently unfavorable circumstances. 



Of all my cultures made last year on the minute scale, in 

 Avhich the spores germinated and the Cystococcus-o.^'s, re- 

 mained alive, by far the most did not last longer than some 

 three weeks ; just as with Bornet, mould prevented the cul- 

 tures being longer extended. 



I then this year began anew some experiments on the minute 

 scale carried on in a somewhat different manner, but still with 

 the object of struggling against the mould-formation, in order to 

 prolong cultures for a longer period. The slides with the 

 spores and algae thereon were first brought into the moist- 

 ened space till there was no further trace of water and spores, 

 and algae had become quite dry (these were always placed upon 

 the slides in a drop of water) . By this plan one of the circum- 



