96 JOHN HILL 



Hill had considerable technical ability and, I think, was 

 capable of greatly advancing anatomical botany ; unfortunately, 

 however, he gave too little time and thought to his investi- 

 gations. 



Physiology. 



The eighteenth century saw the birth of vegetable physio- 

 logy, Hales and Knight being the two great pioneers in this 

 country. The former flourished in the early part of the century, 

 whilst Knight, although born in 1758, published his great work 

 in 1806. 



The chief physiological work of Hill is embodied in a pamphlet 

 of 59 pages, entitled The Sleep of Plants and Causes of Motion 

 in the Sensitive Plant explained, published in London in 1757, 

 a year previous to the appearance of Du Hamel's Physique des 

 Arbres. The paper is in the form of a letter to Linnaeus, and 

 in it the author explains his position with regard to his earlier 

 criticisms of the Linnaean system of classification. 



The work is divided into sections, the first of which consists 

 of a brief historical resume, the opinions of Acosta, Alpinus, Ray 

 and Linnaeus on this subject being alluded to. No mention, 

 however, is made of the observations of Bonnet and of Mairan 

 to the effect that the periodic movements of Alijnosa pudica 

 continued when the plant was kept in prolonged darkness. 



In Section 2, after describing the structure of a leaf. Hill 

 remarks that "Leaves are always surrounded by the air; and 

 they are occasionally and variously influenced by heat, light, 

 and moisture. They are naturally complicated, and they act 

 on most occasions together. We are therefore to observe, first, 

 what effects result from their mutual combinations in a state of 

 nature : and having assigned in these cases the effect to the 

 proper and particular cause, from this power of that agent, 

 whichsoever it is, that acts thus in concert with the rest, we may 

 deduce its operations singly." 



This passage, although not particularly clear, indicates that 

 Hill fully appreciated the fact that the reaction exhibited by 

 a plant organ is a response to the resultant of a number of forces, 

 and that each factor must be examined separately. 



