Ewart . — The Effects of Tropical Insolation . 455 
In order to keep the leaflets of M . pudica fully expanded, 
exposure to light of a certain tonic intensity is necessary ; 
exposure to light of greater intensity than this causing 
a paratonic closure, whilst too feeble illumination causes an 
atonic closure. 
A number of other Leguminosae were examined with 
regard to the paraheliotropic properties of their leaflets, and 
though they vary much in degree of irritability and the 
movement of response is not always of the same kind, never- 
theless the general results, especially with regard to the 
pulvinus being the organ which not only responds to but also 
perceives the stimulus, were essentially similar to those given 
by M. pudica. 
An unnamed Acacia (165 *) is nearly as sensitive as 
M. pudica to both contact and exposure to sunlight. Thus 
the leaflets when lightly tapped rise up and fold together. If 
exposed to full sunlight they fold completely together in two 
to three minutes, expanding fully again in five to eight 
minutes when well shaded. If the pulvini alone are shaded, 
the leaflets expand nearly completely horizontally, and the 
movement is but little slower than it is in Mimosa under 
similar conditions. In sensitiveness to contact and to 
insolation, the leaflets of Robinia Pseud-acacia are almost 
identical with those of the preceding plant. In another 
unnamed Acacia (169 x ) the leaflets are not quite so sensitive, 
a smart rap causing a partial folding, whilst when exposed to 
full sunlight they are not quite so closely approximated 
together and when shaded re-expand more slowly. 
Dalbergia zeylanica , Roxb., though not sensitive to mechan- 
ical irritation, is very nearly as sensitive to, and shows nearly 
as rapid a response to, exposure to full sunlight, as does 
Robinia. 
In Caesalpinia , Dalbergia , and several Acacias, if the leaflets 
are exppsed to full sunlight but the pulvini are shaded, the 
1 The numbers are the Buitenzorg Garden numbers given to enable future 
identification to be made, specific identification being impossible at the time 
owing to the lack of flowers and fruit. 
