BoT.— Vol. I.] PETRCE — VATCRE OF fJCHENS. 211 



for ordinary purposes, but it is ill-suited to culture experi- 

 ments on living organisms, as repeated experience shows. 

 The effect of our distilled water on motile bacteria is 

 marked and immediate. Bacteria actively motile in the 

 media in which they are cultivated in the laboratory will 

 continue to be motile at the same rate if placed in a drop 

 of sterilized tap-water. Transferred either from the cul- 

 ture directly or from sterilized tap-water into which they 

 have been inoculated, to a drop of distilled water, they 

 promptly come to rest and will not recover their motility. 

 The unsatisfactoriness of our distilled water for lichen 

 cultures may, therefore, be attributed to some poison in it 

 and not to the lack of oxygen, for boiled tap-water will be 

 at least as free from oxygen as ordinary distilled water. 



The nutrient agar-agar and gelatine above mentioned 

 were made with tap-water (not distilled water) and had 

 previously been proved to be well adapted to bacteria cul- 

 ture. In the lichen cultures also they were perfectly whole- 

 some, as attested by the only too rapid growth of whatever 

 bacteria were carried into the drops by the spores. 



II. The Germination of Spores. 



The generally practiced method of obtaining lichen- 

 spores for cover-glass cultures is the following: — the thor- 

 oughly cleansed and sterihzed cover-glasses, either dry or 

 with a drop of some sterilized nutrient medium, are so 

 placed that some of the spores discharged from an apothe- 

 cium will strike upon them. The lichen material was pre- 

 pared thus: fresh specimens of R. reticulata, brought into 

 the laboratory from the trees on which they were growing, 

 were brushed and shaken to remove loose dust, etc., from 

 the surface, cut into small pieces, each piece having only 

 one apothecium, and placed on moistened filter-paper in a 

 Petri dish and covered. Near each apothecium, but not 

 touching the lichen, was placed a cover-glass prepared as 

 just described, and supported in such an inclined position 

 that bacteria, etc., which might be floating in the air in the 



