INTRODUCTORY. 
U 
to the perfecting of that system of vessels through which the 
crude fluids from the roots are carried up to the topmost leaf, 
whence, after undergoing chemical transformation in the leaf 
laboratory, it is circulated to all parts of the organism to make 
possible the production of more cells. Each of these has a 
special task, and it becomes invested with cork or wood to 
enable it to become part of the bark or the timber ; or it 
remains soft and develops the green colouring matter, which 
enables it, when exposed to sunlight, to manufacture starch from 
carbon and water. 
This is very similar to what takes place in the human organism, 
where the nutriment taken in is used up in the production of 
new cells, which are differentiated into muscle-cells, bone-cells, 
epidermal-cells, and so forth, building up or renewing muscles or 
nerves, bones or arteries ; but the mechanism of distribution is 
different, the heart-pump doing the work of capillary attraction 
and gravitation. The ancients believed in the Dryads, spirits 
that were imprisoned in trees, and whose life was coterminous 
with that of the tree ; and it will be seen that they had stronger 
physical justification for their belief than they knew. Shake- 
speare relates how Sycorax, the witch-mother of Caliban, im- 
prisoned Ariel in a tree ; and Huxley finely tells us that “ The 
plant is an animal confined in a wooden case ; and Nature, 
like Sycorax, holds thousands of ‘ delicate Ariels’ imprisoned in 
every oak. She is Jealous of letting us know this ; and among 
the higher and more conspicuous forms of plants reveals it 
only by such obscure manifestations as the shrinking of the 
Sensitive Plant, the sudden clasp of the Dionaea, or, still more 
slightly, by the phenomena of the cyclosis.” 
The tree, as we have indicated, gets its food from the air and 
the soil. The rootlets have the power of dissolving the mineral 
salts in the soil in which they ramify ; some authorities believing 
that they are materially helped in this respect — so far as organic 
matter is concerned — by a fungus that invests them with a 
