ENGLISH AGRICULTURE. 205 



means down to three, four, or five successive sections of nine 

 inches each, still refused to grow red clover. There is a 

 standing instance in the garden at Rothamsted in which red 

 clover has been continuously grown for about thirty years 

 without any trouble at all. The ground upon which this 

 successful experiment is proceeding having been for a period 

 of three hundred years a kitchen garden, is therefore no 

 doubt thoroughly well stocked, as in fact was proved by 

 analysis, with both nitrogenous matter and available mineral 

 constituents. Here there is no clover sickness, and the 

 reasoning seems to be in favour of the fact that clover growth 

 is a question of food supply. It appears, however, practically 

 impossible in ordinary farming to keep a soil in a sufficiently 

 rich state to the required depth, neither can we have the 

 constituents of the clover food in a proper condition for 

 securing a continuous growth of clover upon arable land for 

 a series of years. Probably a similar explanation is the most 

 reasonable one as to why we cannot grow sainfoin or flax for 

 an indefinite number of times the food is wanting. It has 

 been held that crops may render the ground unwholesome, or 

 in some way unfit for the growth of similar crops. This view 

 was promulgated under the name of the excretory theory, or, 

 in other words, that there were certain emanations or excre- 

 tions from plants which in some way rendered the soil dis- 

 tasteful to crops of the same kind, but which might render 

 it all the more fit for the growth of other crops. Un- 

 fortunately no proof whatever has ever been vouchsafed as 

 to any emanation or excretion sent out by the roots of plants. 

 The long period which must elapse between certain crops 

 therefore appears to be due to a fact which is not thoroughly 

 explained, namely, that certain crops render the soil unsuit- 

 able for their own description of crop for a considerable 

 period of time. 



A second reason for rotation is that plants feed differently. 



