** But as it has been shown by De
Vries*** that in these latter cases increased growth is preceded by the
increased turgescence of the cells, the difference between the above two
means of movement is much diminished, and consists chiefly in the
turgescence of the cells of a fully developed pulvinus, not being followed
by growth. When the movements of leaves or cotyledons, furnished with a
pulvinus and destitute of one, are compared, they are seen to be closely
similar, and are apparently effected for the same purpose. Therefore, with
our object in view, it does not appear advisable to separate the above two
sets of cases into two distinct classes. There is, however, one important
distinction between them, namely, that movements effected by growth on the
alternate sides, are confined to young growing leaves, whilst those
effected by means of a pulvinus last for a long time. We have already seen
well-marked instances of this latter fact with cotyledons, and so it is
with leaves, as has been observed by Pfeffer and by ourselves. The long
endurance of the nyctitropic movements when effected by the aid of pulvini
indicates, in addition to the evidence already advanced, the functional
import-
* This distinction was first pointed out (according to Pfeffer, 'Die
Periodischen Bewegungen der Blattorgane,' 1875, p.
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