166 



PHYSIOLOGICAL BOTANY. 



PART II. 



the woody parts. For, if both the pith and the corti- 

 cal portions are removed, the effects are not stopped ; 

 whilst, if the woody parts are abstracted, which con- 

 tain the ducts, they cease entirely. 



(2.) Denmodium gyrans. The Desmodium gy- 

 rans is another plant of the same natural order as the 

 sensitive-plants, the motion of whose leaflets is still 

 more striking than in the latter ; for here the motion 

 is continued, without the necessity of applying any 

 external stimulus. The 

 leaves are composed of a 

 pair of small leaflets, and 

 a terminal one of larger 

 dimensions (fig- 150.). 

 The motion consists of a 

 succession of little jerks, 

 produced at intervals of 

 a few seconds. One of 

 the two lateral leaflets 

 is gradually elevated, 

 whilst the other is de- 

 pressed ; and when both 

 have attained the maxi- 

 mum amount of movement in one direction, they begin 

 to proceed in the opposite. At the same time the 

 terminal leaflet becomes inclined by similar inter- 

 rupted movements ; first on one side, and then on the 

 other. 



(3.) Common Berbery. The flowers of the com- 

 mon Berbery contain six stamens, which surround a 

 single piftil. When first expanded, the stamens are 

 inclined back upon the petals or away from the pistil. 

 If the filaments are touched near the base on the in- 

 side, they immediately start forward towards the pistil, 

 so that the anther is brought close to the stigma. In a 

 little time they recover their original position, and may 

 be again stimulated as before. When the anther is 

 ripe, the violence of the motion causes it to burst, and 

 the pollen is projected on the stigma ; and we may 



