THE PATH OF EVOLUTION 



determination of purpose, in seeking or avoiding 

 light, in directing their rootlets towards water, in the 

 movements of the stamens and pistils, and other 

 phenomena of vegetative life, that are as curious to 

 observe as they are difficult to explain. 



In the absence of any tissues or fibres corresponding 

 to the nervous systems of animals, one fails to find an 

 explanation of the movements of the sensitive plant 

 on being touched, or of the closing of the glandular 

 hairs of the Sun-dew (Drosera) upon an insect that 

 lights on the flower, to be quickly digested by the 

 acid pepsin that the plant secretes. The leaves of 

 the Venus Flytrap (Dioncea Muscipula) are fur- 

 nished at their ends with two semi-circular lobes, 

 provided inside with short, sharp bristles or thorns; 

 the lobes have teeth-like projections on their margins, 

 and they close together like the covers of a book. 

 A viscid secretion on the inner surface attracts 

 insects; on alighting thereon, the lobes close suddenly, 

 imprisoning the insect, which dies and is digested. 

 If small pieces of meat or other nitrogenous food are 

 thrown on the open lobes, the same action results; 

 but if sand, fragments of wood, or even amylaceous 

 substances are scattered thereon, they produce no 

 effect, and remain on the open lobes until washed off 

 or blown away. Agitation of the plant, or mechani- 



272 



