148 EXPERIMENTS UPON LEGUMINOUS CROPS 



This did not however arrest the faihire which was in progress 

 at that time. Again, in March 1897 and in July 1899, all the 

 plants were removed by hand, burnt, and their ashes returned, 

 and the surface soil was carefully picked over by hand, to 

 remove the Sclerotia of the fungus Sderotinia trifolioriim, many 

 of which were found. The soil was also dressed with carbon 

 bisulphide as a fungicide, before fresh seed was sown. In 1903, 

 which was a favom*al:)le year for the growth of clover, a fair 

 plant was obtained by re-seeding, and in the spring of 1904 the 

 best crop for many years was cut from this plot. Notwith- 

 standing the repeated failures to grow clover continuously on 

 ordinary arable soil and the increasing- difficulty of maintaining 

 a plant on the rich garden soil, which is the one place where any 

 growth has been continuous, it is noteworthy that when clover 

 grows in a mixed herbage on grass-land it increases in amount 

 from year to year under suitable conditions of manm-ing. It has 

 already been pointed out that on the grass plots in the park, 

 where mineral manures including potash are applied every year, 

 as on Plots 15, 6 and 7, the proportion of leguminous plants, 

 including red clover, increases fi'om year to year, without there 

 being any sign of " clover sickness " setting in. Nor can this 

 result be due to manuring only, for on the small plots in the 

 Hoos field all sorts of variations in the manuring were tried, 

 without enabling the clover to stand. On the grass paths, 

 however, separating these "clover sick" plots on Hoos field, 

 paths which are not more than a yard broad, both red and 

 white clover grow abundantly. Were "clover sickness" due 

 merely to the infection of the plant by Sclerotiula trifolioriim, 

 it is difficult to see how these plants could escape infection 

 when the neighbouring clover plants in the arable land 

 succumb. These and other facts would seem to show that 

 the presence of the fungus Sderotinia trifoUorum is not the 

 determining cause of " clover sickness " ; in many cases it is 

 the direct cause of the death of the clover plants, luit what 

 is not yet understood is why plants on " clover sick " land 

 alon(i succumb to the infection. 



