It thus
appears that the cotyledons of Mimosa are less sensitive than those of the
previously mentioned plants.*
Oxalis sensitiva.--The blades and pulvini of two cotyledons, standing
horizontally, were rubbed or rather tickled for 30 s. with a fine split
bristle, and in 10 m. each had risen 48o; when looked at again in 35 m.
after being rubbed they had risen 4o more; after 30 additional minutes they
were again horizontal. On hitting a pot rapidly with a stick for 1 m., the
cotyledons of two seedlings were considerably raised in the course of 11 m.
A pot was carried a little distance on a tray and thus jolted; and the
cotyledons of four seedlings were all raised in 10 m.; after 17 m. one had
risen 56o, a second 45o, a third almost 90o, and a fourth 90o. After an
additional interval of 40 m. three of them had re-expanded to a
considerable extent. These observations were made before we were aware at
what an extraordinarily rapid rate the cotyledons circumnutate, and are
therefore liable to error. Nevertheless it is extremely improbable that the
cotyledons in the eight cases given, should all have been rising at the
time when they were irritated.
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