CHAPTER V 



MOVEMENTS OF PLANTS — continued 



Movements in relation to Gravitation — Light-seeking a^id Light- 

 avoiding Movements — Rationale of Light -seeking and Light- 

 avoiding Movemejits — The Sleep of Plants — Mr. Francis 

 Darwin's recent Disc7issiojt of Plant Movements — Sum?nary 

 and Conclnsion. 



Movements of Plants in relation to Gravitation. 



— We are so familiar with the fact that stems grow 

 upwards and roots downwards that we perhaps do not 

 think of it as in the least remarkable that one part of a 

 plant should persistently grow against and the other part 

 in the direction of the acting force of gravity. Of course 

 the student may be tempted to ask what roots would do 

 up in the air or what stems would do down in the ground, 

 or how they could grow otherwise than up and down, but 

 these questions are not exactly to the point — which is this, 

 that even when young plants are taken from their natural 

 conditions, when they are turned upside down or grown on 

 a rapidly rotating wheel, still the opposite tendencies of 

 root and stem assert themselves. 



Let us see how the behaviour of roots and stems to the 

 force of gravity is experimentally demonstrated. 



If seeds of peas and beans which have germinated in 



