1216 MESSRS. J. B. LAWES, J. H. GILBERT, AND M. T. MASTERS, 
them the nutriment.”* HellriegelI found that a plant of barley, in rich porous soil 
had made roots of the aggregate length of 128 feet, while a similar specimen in 
coarser, heavier land had only 80 feet; and numerous measurements of a similar 
character have been made by Nobbe in the course of his water-culture experiments. 
In a mixed pasture where a great variety of species is growing, there is a great 
diversity in the natural habit of the plants, irrespective of the direct effect of soil or 
manure. Some roots go much deeper than others; some branch more than others, 
and in this way different plants, as it were, tap different layers of soil, and so utilize 
portions that would be left unused by others. As a general rule, if the root-range of 
any given plant be restricted, the appropriate food may be presumed to be near at 
hand, and in sufficient quantities. If, on the contrary, the root-range is wade, then the 
food is distributed over a wider area.;f 
There is evidence to show that roots by virtue of the acid fluid with which the 
membrane of the root-hairs or of the absorbent cells is saturated have, at least in 
some cases, the power of dissolving, and it may be presumed directly absorbing, 
substances with which they come in contact; § but this point has not been made a 
subject of investigation at Rothamsted. 
It stands to reason that a large production of root-fibrils and root-hairs would exhaust 
the soil in their immediate neighbourhood sooner, and more thoroughly, than a more 
limited development would do. But it must be remembered that long, deeply-rooting 
plants, or plants with thick root-branches, penetrating downwards to a considerable 
depth, may, in the aggregate, produce quite as many or more feeding roots, though they 
may be more widely diffused and not so apparent to the eye. These differences are, in a 
general sense, denoted by the ordinary terms of surface-rooting or deep-rooting plants. 
The surface-rooting plants have usually finely branched root-fibres in great numbers, 
not penetrating very deeply, and liable to be injured by drought or frost. The more 
deeply-rooting species are usually of longer duration, with coarser, stronger, less branched, 
but much more deeply-penetrating roots. Such plants, therefore, are better able 
to withstand drought; first, because they are not so much affected by surface supply, 
and next, because they can obtain moisture from a greater depth and can accumulate 
a larger store of it in their tissues. These differences were well illustrated in 1870, a 
year very remarkable for the drought which prevailed. In that year, as has been 
more fully explained in Part I. (p. 334, et seq.), samples of the surface soil and turf, 
and of the subsoil of some of the experimental plots were taken, and the distribution 
of the roots was examined at various depths down to 54 inches. The plots selected 
* Sachs, ‘Physiologie Vegetale,’ ed. Micheli, p. 196. 
t Hellriegel, Hoffmann’s Jahresbericht, 1864, p. 106. 
J Dureatj he Lamalle, op . cit . 
§ Dietrich, in Hoffmann’s Jahresbericht, vi., 3; Sachs, ‘ Physiologie Vegetale,’ ed. Micheli, p. 208. 
See also Van Tieghem, 1 Traite de Botanique,’ p. 256 [1882], where the action of the root on the soil is 
compared to a process of digestion, a process carried on only in the part of the root covered with 
root-hairs as a result of the contact of their membrane charged with “ sues ” and the particles of soil. 
