436 



Prof. M. Ward. On the 



[Nov. 21, 



and cut sections, comparing the results with similarly prepared 

 normal tubercles : the chief difference was the paucity in bacteroids, 

 and the prominence of the branched filaments in the cells. Similar 

 results were obtaiued by placing a box over beans growing in the 

 garden, and comparing the tubercles of the etiolated plants with 

 those of normal plants beside them. 



In the spring of this year (1889) I started a series of water- cultures 

 of beans, infected artificially by placing the contents of tubercles on 

 their root-hairs, and kept the roots oxygenated by passing a stream 

 of air through the culture liquid for 24 hours at intervals of a few- 

 days : here again the increased growth of the plants — not compen- 

 sated by increased assimilation — seemed to cause the suppression of 

 the tubercles, or the formation of very poor ones only. These experi- 

 ments, carried out on several dozens of plants, lead me to conclude 

 that the organism which induces the development of the tubercles is 

 so closely adapted to its conditions that comparatively slight disturb- 

 ances of the conditions of symbiosis affect its well-being : it is so 

 dependent on the roots of the Leguminosa3, that anything which 

 affects their well-being affects it also. 



Some experiments with peas, which are now being tabulated, may 

 throw some light on the wider question which has been raised of late, 

 as to the alleged connection between the development of these tuber- 

 cles and the increase of nitrogen in Leguminous plants. Thirty-two 

 peas were sown in separate pots of silver-sand, or soil, in five batches 

 of six each, and one of two, and treated in various ways. Six were 

 in garden soil ; six in silver-sand, with culture salts, including a 

 nitrate; six in the same medium' without nitrate; six in the sand, 

 with traces of soil washings or with pieces of tubercles added ; six in 

 sand sterilised by heating ; and two in sterilised sand, to which salts 

 (including nitrogen) were added.. All but those in the thoroughly 

 sterilised medium bore crops ; and these crops have been analysed for 

 me by Professor Green. The soils, water, and other parts are being 

 analysed by Dr. Matthews of Cooper's Hill. I have to thank these 

 gentlemen for the great care and trouble they have kindly taken in 

 this matter. 



My object was to decide, if possible,,, certain points as to the effects 

 of such treatment on the development of the tubercles ; but the 

 experiment may possibly turn out more instructive than was at first 

 thought, and will at any rate suggest a line of inquiry to be followed 

 oat in the coming spring and summer. 



With respect to these plants, I may say that I shall have data show- 

 ing how much nitrogen was present in the medium at the beginning 

 of the experiment ; how much was added ; how much the average 

 seedling pea contained ; and how much the crop contained in each 

 case. The condition of each plant at convenient intervals was 



