232 



Dr. J. B. Lawes and Dr. J. H. Gilbert. [June 19. 



With these great differences in the amounts of produce the botanical 

 character of the herbage has varied most strikingly. Thus, start- 

 ing with perhaps fifty species on the unmanured land, any kind of 

 manure, that is, anything that increases the growth of any species, 

 induces a struggle, greater or less in degree, causing a greater or less 

 diminution, or a disappearance, of some other species ; until, on some 

 plots, and in some seasons, less than 20 species have been observable, 

 and on some, after a number of years, no more than this are ever 

 traceable. 



Even in the first years of the experiments it was noticed that those 

 manures which are the most effective with wheat, barley, or oats, grown 

 on arable land., that is, with gramineous species grown separately, were 

 also the most effective in bringing forward the grasses proper, in the 

 mixed herbage ; and, again, those manures which were the most- 

 beneficial to beans or clover, the most developed the leguminous 

 species of the mixed herbage, and vice versa. It was further observed 

 that there was great variation in the predominance of individual 

 species among the grasses, and also among the representatives of other 

 orders. And even in the second year the differences in the flora, so to 

 speak, were so marked, that a first attempt at a botanical analysis of 

 carefully taken samples of the produce of some of the plots was then 

 made ; in the third year more detailed separations were made ; and, 

 taking advantage of the experience thus gained, pretty complete 

 botanical analyses have since been conducted four times, at intervals of 

 five years, during the course of the now twenty-four years of the experi- 

 ments ; and on several other occasions partial separations have been 

 undertaken. The character and tendency of the results so obtained 

 may be very briefly indicated as follows : — ■ 



In the produce grown continuously without manure the average 

 number of species found has been 49. Of these, 17 are grasses, 4 

 belong to the order Leguminosaa, and 28 to other orders. The per- 

 centage by weight of the grasses has averaged about 68, that of the 

 Leguminosse about 9, and that of species of other orders 23. 



In the produce of the plot already referred to as the most heavily 

 manured, and yielding the heaviest crops, the average number of 

 species found has been only 19, of which 12 — 13 are grasses, one only 

 (or none) leguminous, and 5 — 6 only represent other orders ; whilst 

 the average proportions by weight have been — of grasses about 95 per 

 cent., of Leguminosa3 less than 01 per cent., and of species represent- 

 ing other orders less than 5 per cent. 



On the other hand, a plot receiving annually manures such as are of 

 little avail for gramineous crops grown separately in rotation, but 

 which favour oeans or clover so grown, has given on the average 

 43 species. Of these 17 in number are grasses, 4 Leguminosae, and 

 22 belong to other orders ; but by weight the percentage of grasses has 



