30 J. II. Gilbert— Points in connection with Vegetation. 



The highly nitrogenous leguminous crops, on the other hand', 

 such as peas, beans, clover, and others, are by no means char- 

 acteristically benefitted by the use of direct nitrogenous 

 manures, such as ammonia-salts or nitrates, though nitrates 

 act much more favorably than ammonia-salts. Again, while, 

 under equal conditions of soil and seasons, mineral without 

 nitrogenous manures increase comparatively little the poor-in- 

 nitrogen gramineous crops that are grown separately, such 

 manures, and especially potass-manures, as has been seen, 

 increase in a striking degree, the growth of crops of the legu- 

 minous family grown separately, and coincidently the amount 

 of nitrogen they assimilate over a given area. 



Such, then, is the result obtained in the separate growth, on 

 arable land, of individual plants of 'the different families. 

 Now, in the mixed herbage of permanent grass land, we may 

 have fifty, or even many more species growing together, repre- 

 senting nearly as many genera, and perhaps eighteen or twenty 

 natural orders or families. Of these, the Graminea? generally 

 contribute the largest portion of the herbage; and, on good 

 grass land, if the Legurninosre do not come second, they are at 

 any rate prominent. The degree in which other orders are 

 represented may be very various indeed, according to soil, 

 locality, seas umstances. In Mr. Lawes' park, 



at Eothamsted, nearly eighty species have been observed: but 

 of many only isolated specimens, and it may be stated generally 

 that about fifty species are so prominent as to be found in 'a 

 carefully averaged sample of the hay grown without manure. 



Experiments on the influence of different manures on this 

 mixed herbage were commenced in 1856 ; at which 1 time the 

 herbage was apparently pretty uniform over the whole area 

 selected. About twenty plots, from one-quarter to one-half an 

 acre each, were marked out, of which two have been left contin- 

 uously without manure, and each of the others has received its 

 own special manure, and as a rule the same description year 

 after year— and the experiments have now been conducted 

 over a period of twenty years. 



Under this varied treatment, changes in the flora, so to 

 speak, became apparent even in the first years of the experi- 

 ments; and three times since their commencement, at intervals 

 of five years— namely, in 1862, 1867, and 1872— a carHuilv 

 averaged sample of the produce of each plot has been taken 

 and submitted to careful botanical separation, and the percent- 

 age, by weight, of each species in the mixed herbage determined. 

 Partial separations have also been made in other years. 



Mr. Lawes has contributed a lame case of specimens to the 

 exhibition, which shows the botanical composition of the herb- 



