524 iieN ~ Royal Society :— 
The plan adopted by the Authors in discussing their own experi- 
mental results, was— 
To consider the conditions to be fulfilled in order to effect the 
solution of the main question, and to endeavour to eliminate all 
sources of error in the investigation. 
To examine a number of collateral questions bearing upon the 
points at issue, and to endeavour so far to solve them, as to reduce 
the general solution to that of a single question to be answered by 
the results of a final set of experiments. 
To give the results of the final experiments, and to discuss their 
bearings upon the question which it is proposed to solve by them. 
Accordingly, the following points are considered :— 
1. The preparation of the soil, or matrix, for the reception of the 
plants and of the nutriment to be supplied to them. 
2. The preparation of the nutriment, embracing that of mineral 
constituents, of certain solutions, and of water. 
3. The conditions of atmosphere to be supplied to the plants, 
and the means of securing them; the apparatus to be employed, &c. 
4, The changes undergone by nitrogenous organic matter during 
‘decomposition, affecting the quantity of combined nitrogen present, 
in circumstances more or less analogous to those in which the expe- 
rimental plants are grown. 
5. The action of agents, as ozone; and the influence of other 
circumstances which may affect the quantity of combined nitrogen 
present im connexion with the plants, independently of the direct 
action of the growing process. 
In most of the experiments a rather clayey soil, ignited with free 
access of air, well-washed with distilled water, and re-ignited, was used 
as the matrix or soil. In a few cases washed and ignited pumice- 
stone was used. 
The mineral constituents were supplied in the form of the ash of 
plants, of the description to be grown if practicable, and if not, of 
some closely allied kind. 
The distilled water used for the final rinsing of all the important 
parts of the apparatus, and for the supply of water to the plants, was 
prepared by boiling off one-third from ordinary water, collecting the 
second third as distillate, and redistilling this, previously acidulated 
with phosphoric acid. 
Most of the pots used were specially made, of poreus ware, with a 
great many holes at the bottom and round the sides near to the 
bottom. ‘These were placed in glazed stone-ware pans with inward- 
turned rims to lessen evaporation. 
Before use, the red-hot matrix and the freshly ignited ash were 
mixed in the red-hot pot, and the whole allowed to cool over sul- 
phuric acid. The soil was then moistened with distilled water, and 
after the lapse of a day or so the seeds or plants were put in. 
Very carefully picked bulks of seed were chosen ; specimens of the 
average weight were taken for the experiment, and in similar speci- 
mens the nitrogen was determined. 
The atmosphere supplied to the plants was washed free from 
