1890.] On the Question of the Fixation of Free Nitrogen. 105 



the end of July. Again, as with the peas, the vetches in the pure 

 and sterilised sand showed extremely limited growth. On the other 

 hand, those in pots 2 and 3, with the soil-extract grew, as shown in 

 the photograph, to a very great height ; indeed, higher than those in 

 pot 4 with the garden soil. 



The heights of the plants were — in pot 1, without soil-extract, 

 11^ and 10J inches; in pot 2, with soil-extract, 52^ and 67 inches; 

 in pot 3, also with soil-extract, 61J and 51 inches ; and in pot 4, with 

 garden soil, only 53 and 36 inches. 



But, as in the case of the peas, whilst the plants in pot 4 with the 

 garden soil flowered and seeded, those in pots 2 and 3, with the soil- 

 extract only, did riot, but continued to extend upwards at the expense 

 of the lower parts of the plant. 



There was much less development of root in pot 1, without soil- 

 extract, than in either pots 2 or 3 with it, or than in pot 4 with the 

 garden soil. The main roots descended to the bottom of the pot, and 

 threw out a number of side branches, but there was a marked defi- 

 ciency of root-fibre. Not a single nodule was found. 



In pot 2, with soil-extract, there was, as shown in a photograph, 

 a dense mass of root and root-fibre, which distributed throughout the 

 whole of the soil, though the greatest accumulation was within the 

 first 3 inches of depth. There were numerous nodules, but consider- 

 ably less in quantity than on the corresponding pea-plants. They 

 were mostly single, the greater number being found in the lower 

 layers, which is also contrary to the result with the peas. They were, 

 moreover, generally exceedingly small. 



In pot 3, also with soil-extract, there was also an immense develop- 

 ment of root and root-fibre through the whole area of the soil ; the 

 greatest accumulation being in the upper and lower portions of the 

 pot, with less in the middle. There were many nodules, but very 

 small, and probably fewer than on the roots in pot 2. All the 

 nodules were single, and fairly distributed over the whole root area. 



In pot 4, with garden soil, there was a moderate amount of root 

 and of root-fibre, chiefly within the upper 6 inches of depth ; but 

 there was altogether very much less of root development than in 

 either pots 2 or 3 with the soil-extract. There were many nodules, 

 but all single, and very small ; and they appeared to be flattened, as 

 if exhausted of their contents. 



Here again, then, as with the peas, the very restricted growth in 

 pot 1, without soil-extract seeding, was associated with very limited 

 root development, and with the entire absence of nodule-formation. 

 On the other hand, the very greatly extended vegetative growth in pots 

 2 and 3, with soil-extract, was associated with an immense develop- 

 ment of root and root-fibre, extending throughout the pots, and with 

 the formation of numerous nodules ; which, however, were generally 



