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by my wife and myself on 30 .Taniuiry at lialf past five p. in. at a 

 pot-plant of about 1 M. high. Within 5 minutes after lapping on 

 the stem all the leaflets of the youngest leaf folded upwards close 

 together; the narrow leaflets of the older leaves (in this species 

 bipinnate) folding distinctly upwards in oblique direction. At the 

 beginning of the experiment all the leaflets were nearly quite 

 expanded, whereas 5 minutes after the irritation the youngei' leaves 

 had assumed the nocturnal position. 



When we repeated the experiment next morning at 7 o'clock with 

 pot-plan(s of the same species, all the younger leaflets showed, it is 

 true, a distinct movement indicating irritation, but the older leallets 

 folded upwards only hardly perceptibly, the younger ones on 

 vigorous tapping and shaking assuming almost nocturnal |)o.sition. 



He it noticed that the irritated leaflets not only |)erfbrn.' a movement 

 upwards, but also take an inclined position with regard to the secondary 

 leafstalks, in such a way that the faces of the leaflets remain fairly 

 parallel. 



The determiiuitiou of the species of the experiment plaiu has 

 been xeritied by me and found correct. 



§ 2. Poinciania regia Bojek. — The hitherto uimoticcd 

 extreme irritability of this species, not seldom cultivated on Java 

 as an ornamental tree, was first observed by me with regard to 

 mechanical stimulants (as shaking and tapping), which hitherto had 

 remained unknown, on 1 Februai-y last at .some very young pot-plants 

 gi'own in the Buitenzorg Hortus. When on that date between 8 and 

 9 a.m. I slightly tapped the stem of some of these plants all the 

 leaflets made within few minutes verv obvious movements indicatinc: 

 irritation, whereas in the no]i-irritated plants all the leaves (in this 

 sj)ecies bi|)innate, with narrow leaflets) i-emaine<l in the normal 

 expanded day j)osition. 



After the plants had been left some hours, the leaffets had, at least 

 outwardly, quite i-ecovered frtmi the irritation. At the hand of some 

 sini|)lc? irritation experiments with a young pot-plant of Poiitridiiut 

 I will try a to describe the (piick and very peculiar complex move- 

 ments performed by the leaflets. 



The experiment plant is about 25 cm. high and has 5 quite expanded 

 leaves. They are bipinnate and (in this young specimen) have from 

 5 — 7 pinnae. The pinnae bear from 7—12 pairs of oval, unhaii-ed 

 leallets, of ii-regular width, very short-stalked, oblique at the base, 

 rounded or crenate at the top, the topmost dark green, those at the 

 base [)ale green, and al)oul 1 cm. long. The common petiole has a 



