THE SOUECES OF THE NITROGEN OF VEGETATION, ETC. 537 



The Graminaceous plants of the experiments of 1858 were supplied with a consider- 

 able quantity of combined Nitrogen at an earlier period of growth than those of 1857 

 (see Tables showing the dates of addition, Appendix, pp. 542, 543), and they were not 

 allowed to exhibit such marked signs of decline of vigour before receiving their fresh 

 supplies. There is, however, no marked distinction in the proportion of the total supply 

 appropriated by the plants, and left in the soil, respectively, in the two cases. 



The Graminacese under the title of "1858, A " (those grown in M. G. Ville's case) 

 were treated similarly to the others of 1858, excepting that the combined Nitrogen was 

 given to them at an earlier period of their growth, and they were not allowed to suffer 

 at any time for want of it. We shall notice the difference in result presently. 



In addition to the evidence of the physiological phenomena as bearing upon the 

 amount of growth due to the supply of ammonia, attention should be called to the 

 remarkable character of growth which was manifested. The evidence afforded on this 

 head, is of interest in considering the question of the character of the conditions most 

 favourable to the assimilation of free Nitrogen ; and it also brings to view some remark- 

 able features in vegetable physiology. 



It will be seen, by reference to the Notes in the Appendix, that, shortly after the 

 addition of ammonia for the first time to the Graminacese (1857 and 1858), the plants 

 began to throw out new shoots at the base of the principal stem. It would thus appear 

 that the plant, being supplied at the commencement of its growth with only the limited 

 quantity of combined Nitrogen contained in its seed, had developed a stem commensu- 

 rate with that quantity. But when new quantities of combined Nitrogen were placed 

 at the disposal of the plant, forces were thus called into activity which were greater 

 than could operate through the medium of the original stem. Some of the new shoots 

 have come forth close to the surface of the soil, some at the first, and some at the second 

 nodes. The character of growth in this respect can be best studied by reference to the 

 drawings of the plants given in Plate XV. 



Another and no less remarkable feature was the formation of roots at the second and 

 third nodes above the ground in the case of most of the Graminaceous plants to which 

 ammonia-salt was added as manure (see Plate XV.). These roots came out around the 

 node, and extended downwards — several of them reaching the soil from heights varying 

 from \ to 1^, or even 2 inches, and penetrating it to the bottom of the pot. The most 

 marked instance of this kind of growth was that of the barley represented in fig. 11, 

 Plate XV., and in more detail, with special reference to the points now under con- 

 sideration, in fig. 16, Plate XV. As will be seen in the figures, roots and new stems 

 come from the same node, making the latter a veritable starting-point, or new axis 

 of growth, like the seed in the first instance. The original stems, below these nodes, 

 did not increase much in size beyond what they had attained before the addition of 

 ammonia ; but the stems above the nodes became much larger than the portions below 

 them, as also did those of the new shoots. 



Finally, so long as the conditions of growth of the plants were such that an addi- 



4 d 2 



