BOOK HI.] Introduction. 365 



microscopic examination of the processes which take place in 

 fertilisation could first be made to yield further conclusions, 

 after sexuality itself, the necessity of the pollen to the produc- 

 tion of fruitful seeds, had been proved by experiment ; in the 

 same way the anatomical investigation of wood could only 

 supply material for explaining the mode in which water rises in 

 it, when it had first been ascertained by experiment that this 

 happens only in the wood, and so in other cases. 



The relation between physiology and physics and chemistry 

 suggests similar considerations ; it is necessary to make some 

 preliminary remarks in explanation of this relation, because we 

 often meet with the view, especially in modern times, that 

 vegetable physiology is virtually only applied physics and 

 chemistry, as though the phenomena of life could be simply 

 deduced from physical and chemical doctrines. This might 

 perhaps be possible, if physics and chemistry had no further 

 questions to solve in their own domains ; but in fact both are 

 still as far distant from this goal, as physiology is from hers. It 

 is true indeed, that modern vegetable physiology would be 

 impossible without modern physics and chemistry, as the earlier 

 science had to rely on the aid of the physics and chemistry of 

 the day, when she was engaged in forming a conception of 

 ascertained vital phenomena as operations of known causes. 

 But it is equally true, that no advance which physics and 

 chemistry have made up to the present time would have pro- 

 duced any system of vegetable physiology, even with the aid of 

 phytotomy ; history shows that a series of vital phenomena in 

 plants had been recognised in the i;th and i8th century, at a 

 time when physics and chemistry had little to offer, and were 

 in no condition to supply explanations of any kind to the 

 physiologist. The true foundation of all physiology is the 

 direct observation of vital phenomena ; these must be evoked 

 or altered by experiment, and studied in their connection, 

 before they can be referred to physical and chemical causes. 

 It is therefore quite possible for vegetable physiology to have 



