e causes of specific differences; an influence which,
though slow in its action, does in time, if the circumstances demand
it, produce marked changes.'"[255]

Mr. Henslow adduces observations and experiments by Buckman, Bailey,
Lesage, Lothelier, Costantin, Bonnier, and others, all demonstrating
that the environment acts directly on the plant.

Henslow also suggests that endogens have originated from exogenous
plants through self-adaptation to an aquatic habit,[256] which is in
line with our idea that certain classes of animals have diverged from
the more primitive ones by change of habit, although this has led to the
development of new class-characteristics by use and disuse, phenomena
which naturally do not operate in plants, owing to their fixed
conditions.

Other botanists--French, German, and English--have also been led to
believe in the direct influence of the _milieu_, or environment. Such
are Viet,[257] and Scott Elliot,[258] who attributes the growth of bulbs
to the "direct influence of the climate."

In a recent work Costantin[259] shares the belief emphatically held by
some German botanists in the direct influence of the environment not
only as modifying the form, but also as impressing, without the aid of
natural selection, that form on the species or part of its inherited
stock; and one chapter is devoted to an attempt to establish the thesis
that acquired characters are inherited.

In his essay "On Dynamic Influences in Evolution" W. H. Dall[260] holds
the view that--

"The environment stands in a relation to the individual such as the
hammer and anvil bear to the blacksmith's hot iron. The organism
suffers during its entire existence a continuous series of
mechanical impacts, none the less real because invisible, or
disguised by the fact that some of them are precipitated by
voluntary effort of the individual itself.... It is probable that
since the initiation of life upon the planet no two organisms have
ever been subjected to exactly the same dynamic influences during
their development.... The reactions of the organism against the
physical forces and mechanical properties of its environment are
abundantly sufficient, if we are granted a single organism, with a
tendency to grow, to begin with; time for the operation of the
forces; and the principle of the survival of the fittest."

In his paper on the hinge of Pelecypod molluscs and its development, he
has pointed o