PROGRESS IN PLANT PHYSIOLOGY 87 



has shone strongly on its under surface ; and I have 

 afterwards put obstacles in its way on which ever side it 

 attempted to escape. In this position the leaf has tried 

 almost every method possible to turn its proper surface 

 to the light." Do you notice how close Knight gets to 

 the true reason for these movements ? Observe his 

 phraseology " the leaf tried almost every method 

 possible/' The words suggest at once a conscious effort 

 on the part of the leaf to do something it was prevented 

 from doing by some external agent. Why did not 

 Knight attribute to the leaf the power of perception or 

 " feeling " so clearly suggested by the very words he 

 uses to express the leaf's activities ? But no, he will 

 have none of it ! " I am wholly unable to trace the 

 existence of anything like sensation or intellect in plants/' 

 he says, and yet the thing was staring him in the face ! 

 " As the whole effort here produced appears to arise 

 merely from the light falling on the under surface of the 

 leaf, I cannot conceive how the contortions of its stalk, 

 in every direction, can be accounted for without admitting 

 not only that the leaf possesses an intrinsic power of 

 moving, but that it also possesses some vehicle of irrita- 

 tion." That is precisely what the plant does possess, 

 although Knight's eyes were blinded to it. Yet he saw 

 much that was hidden even from his successors in the 

 same field of enquiry, and what he saw and recorded 

 entitles him to our admiration and respect. 



