Anyhow, it is certain that the lateral
leaflets do not sleep like the terminal leaflets; and in so far they may be
said to be in a functionally rudimentary condition. They are in a similar
condition in relation to irritability; for if a plant be shaken or
syringed, the terminal leaflets sink down to about 45o beneath the horizon;
but we could never detect any effect thus produced on the lateral leaflets;
yet we are not prepared to assert positively that rubbing or pricking the
pulvinus produces no effect.
As in the case of most rudimentary organs, the leaflets are variable in
size; they often depart from their normal position and do not stand
opposite one another; and one of the two is frequently absent. This absence
appeared in some, but not in all the cases, to be due to the leaflet having
become completely confluent with the main petiole, as might be inferred
from the presence of a slight ridge along its upper margin, and from the
course of the vessels. In one instance there was a vestige of the leaflet,
in the shape of a minute point, at the further end of the ridge.
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