ROOT SECRETIONS. 257 



introducing coloring matters into their trunks, is reported 

 to have shown that the coloring matters are thrown off 

 from the roots, and plants growing near them have been 

 poisoned, although the plant colored continued to grow. 

 Report of British Association Meeting, August, 1841. 



A series of experiments on this subject has been going 

 on during five years in the Botanic Garden, Oxford, under 

 the direction of Professor Daubeny. His object is to as- 

 certain, '* in the first place, how many successive years the 

 soil may admit of the growth of the same crop, and, if it 

 becomes deteriorated, at what rate the decrease of produce 

 may proceed ; and, in the second place, what kind of vege- 

 tables will afi;erwards thrive best in soil, which, with refer- 

 ence to this particular crop, has become damaged, or 

 effete. 



*' With a view to determine this, I have set apart, in one 

 portion of our Botanical Garden, a number of distinct plots 

 of ground, of known size, and uniform as to quality. 



*' These were in the first instance enriched with an equal 

 amount of manure, and brought, as nearly as could be 

 done, in every respect into a similar condition. 



** Fifteen of these beds are planted year after year, with- 

 out intermission, with the following crops : viz. potatoes, 

 turnips, barley, oats, poppies [Papaver somniferum), buck- 

 wheat, tobacco {JYicotiana rustica), flax, hemp, endive, 

 clover {Trifolium pratense), mint (^Mentha viridis), beans, 

 parsley, and beet. 



• ''The remaining fifteen beds receive in turn the same 

 crops, but each year a different one is introduced ; so that 

 by comparing the amount of produce obtained each year 

 from the first and second class of beds, — those in which 

 the crop is permanent, and those in which it is made to 

 shift about, — we may be enabled to learn, how much of 

 any actual diminution ought to be attributed to the season, 

 and how much to a deterioration or exhaustion of the soil. 



'* As it is scarcely five years since the experiments were 

 commenced, the progress made has not yet been sufficient 

 to render the results worth quoting ; but should life and 

 leisure be allowed me for bringing them to a conclusion, 

 I trust some inferences may hereafi;«r be deduced of utility 

 to future husbandmen ; although I should be far more 

 sanguine with respect to the benefit that would accrue, if a 

 piece of ground of greater extent were set apart for such 

 experiments, as, under the auspices of any of our great 

 Agricultural Societies, it might not be difficult to effect. 



22* 



