J. H. Gilbert— Points in connection with Vegetation. 29 

 red super-phosphate of lime alone, once every four vears 



or barley, grown consecutively. With super-phosphate ol' lime 



tl t , ,, , , , [ 



it -really in the logmninous crops, and slightly in the wheat 

 immediately following them, we have the average annual yield 



t veai r'to ii ' l.'.u'l I 't l! n 'l l.'v 



wheat or 1 arley grown continuously by mineral manures alone. 



11 ' _ i . ii i - p - _i iev^and the 



wheat, hut the land was tallowed instead, the total yield of 

 nitrogen in the rotation was very much less: the wheat succeed- 

 ing the fallow yielding very little more nitogen than that suc- 



- 

 crops of the rotation- beans or clover— has been succeeded bv 

 a growth of wheat, and assimilation of nitrogen bv it. almost as 

 great as when it has succeeded a year of lali- 

 a period of accumulation from external sources, and no removal 

 by crops. 



One other illustration must be given of the power of 

 plants of the leguminous and some other families to assim- 

 ilate more nitrogen over a given area than those of the 

 gramineous family. But before cut-ring upon the bearing of 

 the results in question on this particular point, it will he neces- 

 sary to digress a little to call special attention to the conditions 

 of the experiments under which the results were obtained : and 

 it is the more desirable to do this, since the most important of 

 Mr. Lawes' contributions to this Exhibition is an illustration of 

 the results I am about to refer to. 



Effects of manure.— I must here forestall a little what T shall 

 have to refer to more fully further on, as to the effects of char- 



botanical families. I will sav briefly, then, that it is found 

 that nitrogenous manures have generally a very striking effect 

 in incivasim,: the crowth of gi . separately 



on arable land, such as wheat, barley, or oats, all of which con- 

 tain a comparatively small percentage of nitrogen, and, as has 

 been illustrated, assimilate a comparatively small amount of it 



