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 production 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 produced 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 17th and 18th 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
