[VoL. 1 
162 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
pheric nitrogen. In the same year, Gautier and Drouin (12) 
reasserted their former conclusion as to the rôle of algæ in nitro- 
gen fixation, holding that the methods of those who adhere to 
the opinion that algæ fix free nitrogen are too faulty to make 
conclusions drawn from them convincing. 
In the work reported by Schloesing and Laurent in 1892 
(32, 33) an attempt was made to reduce the complexity of the 
algal cultures by introducing into a single experiment only one 
or at most a few species of the algæ. All cultures were made on 
600-gram quantities of either a subsoil or quartz sand to which 
was added (except in the two checks) a small quantity of an 
infusion prepared from soils. The cultures were allowed to de- 
velop for from three to six months, and, as in the previous experi- 
ments of these authors, analyses were made both of the contained 
atmosphere and of the soil and algal growth. The chlorophyl- 
lous plants which appeared in the various cultures are described 
as follows: т and 11—essentially a mixture of Nostoc puncti- 
forme Hariot and Nostoc minutum Desmazières, with a few 
colonies of Cylindrospermum majus Kuetz.; 111—almost а pure 
culture of Nostoc punctiforme; tv—Nostoc punctiforme (less 
pure than in ш), one colony of Phormidium papyraceum, and 
a small quantity of Nostoc minutum; v—two mosses—Brachy- 
thecium rutabulum and Barbula muralis; vi—an almost pure 
culture of an Oscillariee and Microcoleus vaginatus, with 
traces of T'etraspora, Protococcus, Stichococcus, Ulothrix, and 
Lyngbya; үп and vir—checks with no growths, or at most 
a few small patches of Phormidium autumnale Gomont and 
Nostoc punctiforme. Both analytical methods showed abun- 
dant nitrogen fixation in the first four cultures but not an ap- 
preciable one in the fifth,—a fact which the authors explain on 
the basis of specific differences in plants in their ability to fix 
free atmospheric nitrogen. The checks showed no appreciable 
fixation. Separate analyses were made of the top-soil layers, 
containing the algal growths, and the deeper layers, the in- 
creased nitrogen being found in the algal stratum,—a fact which 
the authors consider important in proving that the alge were 
responsible for the free-nitrogen fixation. In conclusion, Schloe- 
sing and Laurent admit the possibility that the bacteria present 
in the cultures had something to do with the fixation of free 
