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disease. In the first place, certain physical differences can be traced in the 

 tissues of the plants ; just as high nitrogen results in a weakness of straw 

 in cereals, due to a long-jointed soft stem, so the cuticle of the leaf and the 

 cell walls of the leaf tissue are measurably thinner when the plant has been 

 grown with an excess of nitrogen. The cause is, however, more probably 

 to be found in some alteration in the composition of the cell sap, which 

 renders it a better medium for the growth of the fungus in question. It 

 has been found, for example, that spores of the Uromyces betae will grow 

 freely upon a bruised surface of the mangold leaves grown with excess of 

 nitrogen, but make no headway when sown upon a similarly bruised 

 surface of the leaf of a normally matured plant. 



The softness of tissue that is induced by large applications of nitro- 

 genous manure — most markedly by nitrate of soda, because of its imme- 

 diate availability — is recognized in other ways ; for example, cabbages and 

 similar vegetables grown rapidly with nitrate of soda are preferable for 

 immediate consumption because of their tenderness, but in the market they 

 bear a bad reputation, because the same softness of tissue leads to rapid 

 wilting and a faded appearance when the vegetables have been cut for 

 some time and have experienced the usual amount of rough handling in 

 transit. 



Potash. — On the grass plots at Rothamsted another striking effect of 

 potash manuring is also very manifest. 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 always characterized 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 mangolds on the 

 Barn field were replaced by Swede turnips, they grew with considerable 

 vigour and remained perfectly healthy, but on the potash-starved plots 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 marked off the whole plot very distinctly, especially after the 

 first frosts had taken place. 



