68 
SIR J. B. LAWES AND PROFESSOR J. H. GILBERT ON THE 
stitute a supply of reserve material for growth; and secondly that the investigations 
of Tschirch and Brunchorst, prove that the nodules have no external communication 
with the soil. As to the latter objection, it may be observed, that Professor Marshall 
Ward has recently shown that, on the death of the nodules, the micro-organisms become 
distributed within the soil; and further, that in the case of Hellriegel’s experi¬ 
ments it was the organisms themselves, or their germs, that he supplied to the soil. 
It must be admitted that Hellriegel’s results, taken together with those of 
Berthelot and others, do suggest the possibility that although the higher plants may 
not possess the power of directly fixing the free nitrogen of the am, lower organisms, 
which abound within the soil, may have that power, and may thus bring free nitrogen 
into a state of combination within the soil in which it is available to the higher plants 
—at any rate to members of the Papilionaceous family. At the same time it will be 
granted, that further confirmation is essential, before such a conclusion can be accepted 
as fully established. 
Since the above was written. Dr. Wilearth, who was associated with Professor 
Hellriegel in the experiments which have been described, has given an account of a 
subsequent series of experiments which were made in 1887. Under the title of “Ueber 
Stickstoffaufiiahme der Pflanzen,” he gave the results at the meeting of the Natur- 
forscher-Versammlung, at Wiesbaden, in September, 1887, and a short account of them 
was published in the ‘ Tageblatt,’ pp. 362-63, and also in ‘ Versuchs-Stationen,’ vol. 34, 
1887, pp. 460-61, of which the following is a pretty full summary ;— 
He states that the previous experiments had shown, that the Gramineae, the 
Chenopodiaceae, the Polygoneae, and the Cruciferae, take their nitrogen from the soil, 
and that their growth was proportional to the available supply of nitrogen. The 
Papilionaceae on the other hand take their nitrogen from the air, and grow quite 
normally in an absolutely nitrogen-free soil, provided a very small quantity of 
cultivated soil be added. He further states that they have now repeated the experi¬ 
ments in the same way, and that the results fully confirm the conclusions before 
arrived at as above stated. 
The new experiments were made with oats, buckwheat, rape, peas, serradella, and 
lupins. The experimental soil was a pure sand, entirely free from nitrogen. Each 
pot contained 4 kilog. of this sand, to which were added the necessary mineral 
constituents. All the plants grew until the nitrogen of the seed was used up. Then 
to each pot a small quantity of the turbid watery extract of a surface soil was added, 
the quantity representing 5 c.c. of the soil, and containing from 0'3 to 0‘7 millig. 
nitrogen. After this the difierent plants exhibited very great differences in growth. 
Neither the oats, rape, nor buckwheat showed any effect from the addition of the soil- 
extract, but remained in the condition of “nitrogen-hunger.” On the other hand, the 
Papilionacem after a time recovered from their nitrogen-hunger, suddenly became 
dark green, and then grew luxuriantly up to ripeness. In experiments in which the 
soil-extract was sterilised by boiling, there was no such result. Peas grew well under 
