ASPECTS OF AN OLD AGRICULTURAL QUESTION. 269 



trolled experiments with apparatus such as that used by- 

 Laurent and Schloesing, and with the bacteria employed 

 not only cultivated pure (Caron did that), but examined 

 rigidly by the best bacteriological methods. 



In any case, as even this brief summary of recent re- 

 sults will show, the problem of the relation of the agri- 

 cultural plant to soil and air is taking new turns, and it 

 remains to be seen how far the new departures will carry 

 us. If symbiosis, whether intimate, as in the case of 

 leguminous plant and bacteroid, etc., of algse and bacteria, 

 or remote (for the carbo-hydrates necessary are merely not 

 handed over directly — a point which only makes the sym- 

 biosis disjunctive), as in the case of Winogradsky's and 

 Berthelot's bacteria, is so powerful an advantage in the 

 struggle for existence, we may well expect that further 

 research will yield much. 



After all symbiotic algae and bacteria are merely 

 lichens — bactero-lichens if you will ; if it turns out that 

 some of the lichens on the bare crags and peaks of primi- 

 tive rocks behave towards free nitrogen as those examined 

 by Kossowitsch did, we may hope to approach the solution 

 of even deeper problems concerning the circulation of 

 nitrogen in Nature. 



Many other problems are before us to which the above 

 results and speculations give new interests. What are the 

 nostoc filaments doing in the cavities they regularly occupy 

 in gunnera, and in the remarkable apogeotropic roots of 

 cycads, where they seem to have made themselves as much 

 a part of the tissues as in a lichen ? What effects do they 

 produce on the physiological activity of the colourless cells 

 between which they intercalate themselves ? Are these 

 cycad-nostocs accompanied by bacteria, as Reinke and 

 Schneider observed in some cases ; and, if so, have we the 

 same thing here going on in the tissues of higher plants as 

 in the alo-ae and bacteria of Kossowitsch ? Numerous 

 other questions of the same kind arise concerning nostocs 

 and other algae habitually embedded in liverworts and 

 vascular cryptogams, and among the various aquatic 

 plants there are many more examples of mysterious sym- 



