1020 



THE NATURE BOOK 



intimate relations between all living 

 things. 



In the old days it was often suggested 

 that plants cannot feel, although on 

 what grounds the assertion was made it 

 is not eas\' to see. Reduced to its simplest 

 possible form, the ability to feel merely 

 indicates the power of response to a 

 stimulus. The pupil of the human eye 

 is so delicately adjusted that it can feel 

 the influence of light, contracting when 

 an increase in the amount of illumination 

 takes place, and expanding when the 

 light-rays are few in number. It is easy 

 to prove that a plant can feel the light. 

 Place a healthy specimen in front of a 

 window in such a position that the light 

 can only reach it from one direction. In 

 a few days the growth of the plant is 

 entirely altered ; its upright bearing 

 goes, and it leans over so that the upper 

 surface of its foliage may be fulh^ exposed 

 to the stimulating rays. The same point 

 may be very strikingly illustrated if a 

 small collection of seedlings is grown in a 



box wiili a single aperture, when it is 

 seen that all the young stems turn towards 

 the path of the light. Some little plants 

 are astonishingly sensitive even to very 

 feeble illumination. 



Darwin showed that the cotyledons of 

 Phalaris became " curved towards a 

 distant lamp which emitted so little 

 light that a pencil held vertically close 

 to the plants did not cast any shadow 

 which the eye could perceive on a white 

 card." In another experiment it was 

 shown that if seedlings kept in a dark 

 place were laterally illuminated by a taper 

 for a minute or two at intervals of three- 

 quarters of an hour, the little stems leaned 

 over to the direction from which the 

 intermittent light had come. Normally 

 the extreme sensitiveness of leaves to the 

 action of light is well seen in the case of 

 climbing plants, particularly when the 

 specimens are growing up a wall. Even 

 though the effort may entail considerable 

 distortion of stalk, the leaves are in- 

 variably brought round so that the face 



THE SENSITIVE HLANT. 



