i;o 
NATURE NOTES. 
plant-structures are in adaptation to their needs. For when one 
studies the structures and functions of roots, stems, leaves, 
flowers and fruits, it becomes perfectly clear that these structures 
and their functions are in harmony with their surroundings ; 
that is to say, e.g., the root is adapted for absorbing water, 
mineral, and other matters from the soil ; that the stem is 
adapted to support the plant or tree and convey the fluids up- 
wards ; that the leaves are adapted to imbibe carbonic acid 
from the air and to decompose it and then convert it into starch, 
as well as to transpire or exhale large quantities of superfluous 
moisture ; also to respire, as we do ; for it is as necessary for 
plants to breathe as much as animals, and if they be prevented 
doing so they will be asphyxiated too. Then, again, all the 
minute details of the structure of flowers are so many adapta- 
tions to the requirements of setting seed, by which the plant 
can be reproduced. 
Hence we can recognise two “ends” in plant-life, viz., a 
healthy vigorous growth of the individual, and the production of 
plenty of good seed on the event of its death. We soon see, 
therefore, how every phase of its existence is in harmony with, 
or “correlated” to its environment, and under that term is 
included soil and its ingredients, air, moisture, temperature, 
light, &c. ; and in the case of flowers, the visits of particular 
insects, if they be required, as is often the case, if not, then it is 
the wind, or else the flowers are so formed as to be independent 
of both wind and insects, and are specially constructed to be 
able to fertilise themselves. Such is the environment taken in 
its widest sense, and we repeat the question : How has any plant 
become adapted to its environment, so that all its various organs 
can perform their several functions in perfect harmony with the 
various features of this environment ? 
There are two ways of answering this question. First, to 
examine plants in nature which can, and often do, live under very 
different conditions or surroundings; as, e.g., under water or on 
land and in air, and watch them to see how they change. 
These might be called natural experiments. We may also 
cultivate plants in very different and artificially prepared soils, 
&c., from those in which they naturally grow in the wild state. 
Such will be artificial experiments. 
Secondly, there is a line of argument of great value, which 
will be emphasized further on by illustrations. It is, that when 
innumerable cases occur of certain phenomena always re-appear- 
ing under similar circumstances or conditions, we are justified 
in drawing the conclusion that there is a distinct cause and 
effect, even though we may not be able to verify our inference 
or deduction by actual experiment. In many cases we can, it 
is true, supply the conditions, and then we discover that we 
can produce at will the same effects as those we see appearing 
in nature under similar circumstances. This of course greatly 
strengthens the argument, but it is not absolutely necessary for 
the establishment of the truth. 
