SENSITIVE PLANT. 421 



1089. If an irritant is applied to a single leaflet, the opposite 

 one may be the only other affected ; or, if the effect is more pro- 

 nounced, all the leaflets on a single division of the leaf may be 

 closed without affecting any on the other branches. But if a still 

 sharper impulse is given, not only will all the leaflets on a single 

 leaf close, but other leaves on the plant may be affected. Thus 

 it is possible by applying a hot needle to a single leaflet to affect 

 all those on a small plant. A drop of strong sulphuric acid acts 

 in the same way. 1 



When a leaf of Mimosa is separated from its plant by a sharp 

 cut through its pulvinus, and is at once placed in a saturated 

 atmosphere, it soon recovers its normal expanded condition ; if 

 now it is touched the leaflets will collapse as usual, and at the 

 moment of closing a drop of water can be seen exuding from the 

 cut surface. According to Pfeffer it is possible to observe that 

 the water comes from the parenchyma of the lower half of the 

 pulvinus. 2 



1090. According to Bert, 8 who made use of a thermo-electric 

 apparatus, the pulvinus of a leaf of Mimosa in its normal condi- 



1 For a study of the transmission of the shock, see Pfeffer, Pringsheim's 

 Jahrbiicher, ix., 1873, p. 308. 



Some of the effects produced by irritants upon the hairs of certain insectiv- 

 orous plants have been already described. The phenomena of aggregation 

 then alluded to must be now treated more in detail. It is described by Pfeffer 

 in the following words : " Suddenly the contents of the cell acted on become 

 clouded by a separation of minute particles which aggregate to form masses. 

 These masses consist essentially of albuminous matters, which, from their col- 

 lecting the coloring substance in the cell-sap, become tinged. The whole 

 process of aggregation takes place in the cell-sap." 



Pfeffer points out the curious fact that while ammonic carbonate, without 

 any other irritant, will cause this aggregation, acetic acid will make it 

 disappear. 



Such changes as aggregation and variations in turgescence are connected in 

 some way, not yet understood, with the imbibition power of protoplasm for 

 watery fluids. The mechanical or chemical irritants which temporarily dimin- 

 ish the capacity of protoplasm for retaining within the cell the maximum 

 quantity of water will produce a distinct effect upon the tension of the cell- 

 wall, and result in a change of its size or form, or both. The irritation thus 

 caused can be transmitted to a distant part. The intimate relations which 

 exist between the young cell-wall and the protoplasmic, lining must not be 

 overlooked in any consideration of the subject of sensitiveness in plants. 

 Lastly, the continuity of protoplasm in many mobile and sensitive organs must 

 be borne in mind in the consideration of this subject. 



2 Pflanzenphysiologie, ii., 1881, p. 237. See also Pfeffer's Physiologische 

 Untersuchungen, 1873, p. 32. 



8 Comptes Eendus, Ixix., 1869, p. 895. 



