56 Bristol. — On the Alga- Flora of some Desiccated 
and on the soil itself, but up to the present too little is known on the subject 
to make any very definite statements in this direction. 
It was thought by Frank 1 and by Schloesing and Laurent 2 that 
algae in the soil had the power of fixing atmospheric nitrogen, but later 
experiments by Kossowitsch 3 showed conclusively that algae by them- 
selves are quite unable to carry on these activities. Kossowitsch suggested, 
on the contrary, that nitrogen fixation was the result of bacterial activity, 
and definitely proved this to be true in a few of his cultures. He observed, 
however, that the presence of certain algae in the soil is highly advantageous 
to nitrogen fixation, and concluded that there exists a symbiotic relationship 
between the algae and bacteria of the soil as a result of which nitrogen 
compounds are added to the soil. From the observation of Berthelot 4 
that an increase in the nitrogen content of the soil does not continue unless 
fresh organic material is added to the soil, and that of Gautier and Drouin 5 
that organic compounds destitute of nitrogen serve to stimulate nitrogen 
fixation in the soil, together with his own observation that the addition of 
sugar to certain cultures containing algae and bacteria made little difference 
to the amount of nitrogen fixed by the organisms, though in the absence of 
algae the difference was very considerable, Kossowitsch concluded that the 
bacteria were able to use certain organic compounds supplied by the algae. 
He suggested that the mucous sheaths always observed to be present round 
those algae having the greatest effect on nitrogen fixation probably provide 
the carbohydrate needed by the bacteria for growth ; in return the algae 
are supplied with the nitrogenous substances without which they are unable 
to develop. 
Further experiments by Bouilhac and Giustiniani 6 showed that in 
sand completely destitute of organic matter and of nitrogen compounds 
a mixture of soil-bacteria and algae are not only able to develop normally, 
but also to enrich the soil with nitrogen sufficiently to support the growth of 
1 Frank, B. : ( a ) Ueber den experimentellen Nachweis der Assimilation freien Stickstoffs 
durch erdbodenbewohnende Algen. Ber. der D. Bot. Ges., vii, 1889, pp. 34-42. 
( b ) Ueber den gegenwartigen Stand unserer Kenntnisse der Assimilation elementaren Stickstoffs 
durch die Pflanze. Ber. der D. Bot. Ges., vii, 1889, pp. 234-47. 
(c) Frank, B., and Otto, R. : Untersuchungen iiber Stickstoff- Assimilation in der Pflanze. Ber. 
der D. Bot. Ges., viii, 1890, pp. 331-42. 
2 Schloesing, fils, and Laurent, E. : Recherches sur la fixation de l’azote libre par les plantes. 
Ann. de l’Institut Pasteur, vi, 1892, pp. 65-115. 
3 Kossowitsch, P. : Untersuchungen iiber die Frage, ob die Algen freien Stickstoff fixiren. Bot. 
Zeit., 1894, Heft 5, pp. 98-116. 
4 Berthelot, M. : Recherches nouvelles sur les microorganismes fixateurs de l’azote. Compt. 
Rend., cxvi, 1893, pp. 842-9. 
B Gautier and Drouin : Recherches sur la fixation de 1 ’azote par le sol et les vegetaux. Compt. 
Rend., cvi, 1888, pp. 754, 863, 944, 1098, 1174, 1232, 1605. 
6 (a) Bouilhac, R. : Sur la fixation de l’azote atmospherique par Passociation des algues et des 
bacteries. Compt. Rend., cxxiii, 1896, pp. 828-30. 
(b) Bouilhac, R., and Giustiniani : Sur une culture de sarrasin en presence d’un melange d’algues 
et de bacteries. Compt. Rend., cxxxvii, 1903, pp. 1274-6. 
