dissolved at the points of union, so 
{hs 
oe he Life of the Plant. 165 
come into intimate contact with all the unevennesses of the 
adjacent solid particles, and afterwards, by the hardening of 
the membrane, actually unite with them : 
(Fig. 345). And since experiment has 
shown that the cell-sap is almost always 
acid, its passage into the ground causes 
the particles of soil with which the 
root-hairs have united to be gradually 
that they can then be taken up into the 
plant. | 
- The mode of nutrition of parasites is 
different from this. The roots of the 
more highly organised parasites, such 
as the mistletoe and the broom-rape, ae. ee 
Orobanche, penetrate ito another plant . a eae ee 
which is termed their Zost (Fig. 346), have taken up minute 
and take up from it nutrient substances Ce fF aul ae 
which have already been to a certain 2 (% 80) 
extent assimilated. The lower parasites, such as certain 
Fungi, on the other hand, pierce by their cells the mem- 
branes of other cells, in order to live in and on them 
(Fig. 347). The mode of absorption of food-material and 
of the nutrition of saprophytes [or plants which live on 
decaying organic substances], such as Monotropa Hypo- | 
pitys and certain Orchideee, is still in doubt. ‘The charac- 
teristic of these plants is that their absorptive organs take 
up certain products of the decomposition of organic sub- 
stances, termed humus, and bring them again into requisition 
for nutrition, after undergoing some change. 
Plants do not absorb the nutrient substances which are 
adapted to them unless presented to them in a suitable form ; > 
they do not for example, imbibe the free nitrogen of the 
atmosphere. Experiments, into the details of which we cannot 
enter, have given on this point the following results :— 
The source of the carbon in those plants which contain 
