earth. In accordance with these conclusions, a considerable difficulty in
the way of evolution is in part removed, for it might have been asked, how
did all these diversified movements for the most different purposes first
arise? As the case stands, we know that there is always movement in
progress, and its amplitude, or direction, or both, have only to be
modified for the good of the plant in relation with internal or external
stimuli.

Besides describing the several modified forms of circumnutation, some other
subjects will be discussed. The two which have interested us most are,
firstly, the fact that with some seedling plants the uppermost part alone
is sensitive to light, and transmits an influence to the lower part,
causing it to bend. If therefore the upper part be wholly protected from
light, the lower part may be exposed for hours to it, and yet does not
become in the least bent, although this would have occurred quickly if the
upper part had been excited by light. Secondly, with the radicles of
seedlings, the tip is sensitive to various stimuli, especially to very
slight pressure, and when thus excited, transmits an influence to the upper
part, causing it to bend from the pressed side. On the other hand, if the
tip is subjected to the vapour of water proceeding from one side, the upper
part of the radicle bends towards this side. Again it is the tip, as stated
by Ciesielski, though denied by others, which is sensitive to the
attraction of gravity, and by transmission causes the adjoining parts of
the radicle to bend towards the centre of the earth. These several cases of
the effects of contact, other irritants, vapour, light, and the
[page 5]
attraction of gravity being transmitted from the excited part for some
little distance along the organ in question, have an important bearing on
the theory of all such movements.