1890.] On the Question of the Fixation of Free Nitrogen. 107 



In pot 1, without soil- extract, and very restricted above-ground 

 growth, there was coincidently very little root development. The 

 main roots descended far down the deep pot almost without branching, 

 but at the bottom a number of branches, and a mass of fibre were 

 produced. The root-fibres were fleshy and succulent. No root 

 swellings or nodules were found. 



In pot 2, with the lupin-soil-extract seeding, there was, on the 

 other hand, a very great development of root. Branches were thrown 

 out throughout the whole length ; and at their ends masses of fleshy 

 fibrils were formed, which were thickly coated with root-hairs. On 

 the main root of one plant, 3 inches down, there was a large swelling 

 or nodule the size of a field bean ; 4 inches lower there were three 

 smaller ones on a side branch ; 10 inches down there were three as 

 large as peas ; and lower still there was another small swelling, more 

 like the nodules found on other plants. The other plant had less root 

 growth. One and a half inch down there was a swelling the size of a 

 small pea ; and 4t? inches lower there were three swellings, one as 

 large as a bean, and the others about the size of a vetch seed. These 

 swellings on the -lupin-roots, which were all on the main roots or 

 thicker branches, are very different in appearance from the nodules 

 on the pea and vetch-roots. They are, as described, swellings, en- 

 casing the root where they grow. 



In pot 3, also with the soil-extract seeding, one plant, as an 

 enlarged photograph shows, developed an immense amount of 

 branching root, with a great deal of root- fibre, which extended 

 throughout the whole soil, bat to a greater degree in the lower than 

 in the upper half of the pot. The main root was woody near the 

 top. The lower root-fibres were fleshy, and thickly coated with root- 

 hairs. There were several swellings or nodules on the main root 

 below 5 inches; and lower down, on a root-branch, there were several 

 swellings ; there being in all twelve on this plant. On the smaller 

 and more meagrely rooted plant, about 10 inches down, there were 

 also two bunches of small nodules, and three single nodules ; and a 

 little lower, on a side branch, another small nodule. With regard to 

 the great development of root-hairs on the fine fibrils of the roots in 

 both pots 2 and 3, with quartz sand and soil-extract seeding, it may 

 be supposed that this was an effort to acquire mineral nutriment, 

 in quantity commensurate with the large amount of nitrogen fixed, 

 and available to the plant. 



In pot 4, with the lupin-sand, the distribution of root was very 

 different from that in pots 2 and 3, with the soil-extract. The main 

 root, at a depth of 2 inches, threw out many thread-like branches, at 

 the end of each of which there was a bundle of fine fibre. The 

 lower fibres became thicker, and were white and fleshy ; but they 

 were without the marked development of root-hairs observed in such 



