546 History of the Doctrine of [BOOK in. 



laws were on the whole unsatisfactory, all such explanations 

 were looked upon as impossible and even absurd, while it was 

 forgotten that the vital force, which was to explain everything, 

 was a mere word for everything that could not be explained in 

 the life of organisms. This vital force was personified, and 

 seemed to assume a really tangible form in the movements of 

 plants. But the moment that a phenomenon was handed over 

 to this force, all further investigation was abandoned ; the idea 

 with regard to phytodynamical phenomena especially was that 

 of the peasant, who could only explain the movement of the 

 locomotive by supposing that there was a horse shut up in it. 

 Moreover the knowledge of the inner structure of plants was at 

 its lowest point at the end of the 1 8th century ; the spiral 

 threads which could be unwound were the only structural 

 element whose form was to some extent understood, and their 

 hygroscopic movements were supposed to be due to a combina- 

 tion of the pulsations of the vital force with the spiral tendency 

 of the plant. At the same time whole bundles of vessels were 

 taken for spiral fibres, or were supposed to consist of them, and 

 these were thought to be vegetable muscles, which contract 

 under the influence of various kinds of irritation, and so cause 

 the movements in the organs of plants ; but it was forgotten 

 that in the organs which exhibit the most striking movements, 

 such as sensitive leaves and leaves that suffer periodical 

 changes of position, these ' muscles ' occupy a central position 

 which unfits them for the function ascribed to them. It would 

 be unprofitable and wearisome to give many examples of what 

 is here stated, though many might easily be collected ; it will 

 suffice to quote some sentences only from Link's ' Grundlehren 

 der Anatomic und Physiologic' of 1807; they are particularly 

 instructive, because Link declared against the nature-philosophy 

 and professed to be on the side of inductive science. Under 

 the head of movements of plants, he discussed geotropic curva- 

 tures and other movements in the superficial manner of the 

 time and only to come to the conclusion, that the direction of 



