166 
FOOD OF PLANTS, AND HOW THEY TAKE IT. 
supposed the food was carried in solution in rain-water and 
carbonic acid to the roots of plants, 'which were thus like 
sponges, half in the moist ground, half in the air, continu¬ 
ously absorbing by their roots, and evaporating by their 
leaves. Whatever was in solution passed with the water 
into the roots, and by the process of nutrition was appro¬ 
priated by the plants. The soil and the plant being passive, 
. . . . we believed that the water was the carrier of the 
most remote elements of the soil to the immediate presence of 
the plant. . . . But all this has been a great mistake. 5 ’ 
Examinations of rain-water that has passed through the 
soil and collected by drainage, of spring-water, and of river- 
water, show that they do not take up those substances that 
are known as plant-food in any considerable quantity. 
“ These substances are present in the soil, in a condition fit 
for absorption by the rootlets of plants, though not them¬ 
selves soluble or removeable by the rain-water, until the soil is 
saturated with them. It is more than probable that the 
majority of our cultivated plants receive their nourishment 
directly from those portions of the soil which are in imme¬ 
diate contact with their rootlets, and that they die when 
their food is presented to them in solution. The action of 
concentrated manures, burning the young plants, seems to 
support this supposition. 55 
“ . . . It follows that the plants must themselves play 
some peculiar part in the absorption of their food. As 
organized living structures, their existence is not quite de¬ 
pendent on external causes. . . . They select from 
the soil those substances which they require, but which can 
only pass into their interior by the co-operation of a cause 
which resides within their rootlets. . . . It is very diffi¬ 
cult to explain in what way plants act in causing the solu¬ 
tion of mineral substances. As a matter of course, water is 
indispensable in the operation. 55 
Green manures have been highly extolled, and not with¬ 
out cause. Though they can add nothing to the mineral 
wealth of the soil, they add carbonaceous and nitrogenous 
matters, having collected the elements from the atmosphere; 
further, they bring up mineral matters from the subsoil, 
which they penetrate with their long roots, and in their 
decay they enrich the upper soil for the use of cereals and 
such other plants as chiefly occupy this portion as their 
range in search of food. It will be readily guessed that 
annual plants need to have their food more accessible than 
perennials, such as trees, which have a wide and deep range. 
Before concluding this paper, I ask to thank one of the 
