vi.l EFFECT OF POTASH UPON GRASS LAND 173 



only 22 per cent, and 15 per cent., the higher proportion 

 being where magnesia and soda, which attack the potash 

 reserves in the soil, are applied. It should be noticed 

 that the large amount of phosphoric acid received by 

 these two latter plots does not result in any great 

 stimulus to the leguminous plants, which constitute 7-5 

 per cent, of the herbage of the unmanured plot. Where 

 nitrogen is applied and potash omitted, no leguminous 

 plants are to be found. 



On these grass plots another very striking effect of 

 potash manuring is also very manifest, which confirms, 

 on a large scale, the experiment of Hellriegel and 

 Wilfarth's already quoted. On the potash-starved plots 

 the grasses fail to a large extent to develop any seed, 

 and the heads are soft and barren, presumably because 

 of the deficiency in carbohydrate formation. For the 

 same cause the straw, not only of the grasses, but also 

 on the similarly manured wheat and barley plots, is 

 always weak and brittle when potash is wanting. The 

 plants of the potash-starved plots at Rothamsted are 

 also characterised by certain other appearances, which 

 to a less degree are to be observed in nature where the 

 soil is naturally poor in potash, as on many peaty and 

 sandy lands. The grass has a dull colour, partly due 

 to a deficiency of chlorophyll and its substitution by 

 a certain amount of a red colouring matter along the 

 stems, and partly because the tops of the grass blades 

 show a great tendency to die off for an inch or two and 

 leave a brown withered end. When in 1908 the man- 

 golds on the Barn field were replaced by Swede turnips, 

 they grew with considerable vigour and remained per- 

 fectly healthy on the potash-starved plots, except that 

 the leaves in the autumn showed a flecked appearance, 

 especially towards the margins, where a good deal of 

 the leaf tissue had a yellow brown papery look which 



