VITAL PRINCIPLE. 11 



The term of duration is very different in different spe- 

 cies. While many mushrooms and insects are but the 

 beings " of a summer's day, 11 the stately oak and the vora- 

 cious pike outlive centuries. In general, when the pre- 

 vious growth of an organized body has been slow, the pe- 

 riod of decay is protracted in proportion ; and, when ma- 

 turity has been quickly attained, decay as rapidly suc- 

 ceeds. 



2. POSSESSED OF IRRITABILITY. There is in this power 

 which we are now consideringj a disposition to be acted 

 upon by different external objects, and to exhibit the influ- 

 ence which these exercise by contractile or expansive move- 

 ments. This faculty is termed Irritability. It appears to 

 reside in the fibrous part of organized bodies. Plants ex- 

 hibit this power in a very remarkable manner^ upon expo- 

 sure to the light of the sun, bending their stems, and turn- 

 ing their leaves in various directions, according to the inten- 

 sity and incidence of the rays. The pinnated leaves of cer- 

 tain plants exhibit the same power, when touched by any ex- 

 traneous body, the various leaflets collapsing in rapid suc- 

 cession. This is well displayed in Mimosa pudica and sen- 

 sitiva, Smiihia sensitiva, and some others. TheHedysarum 

 gyrans, or Moving Plant, as it has been termed, exhibits 

 a motion in its leaves of a still more remarkable kind, re- 

 quiring a very warm still atmosphere for its production. 

 The leaf is ternate, and the lateral leaflets approach and 

 recede from one another, in a manner irregular as to time 

 and co-operation. But the example of vegetable irritability 

 which is most accessible in this country, is exhibited by the 

 Barberry-bush. Sir JAMES EDWARD SMITH, who first ob- 

 served the phenomenon, thus expresses himself: " In this 

 (flower) the six stamens, spreading moderately, are sheltered 

 under the concave tips of the petals, till some extraneous bo- 

 dy, as the feet or trunk of an insect, in search of honey, 



