CHAPTER III. 



HISTORY OF THE DOCTRINE OF THE MOVEMENTS OF 

 PLANTS (PHYTODYNAMICS). 



IT will scarcely be doubted at the present day, that the 

 mechanical laws of growth, of geotropic and heliotropic curva- 

 tures, of the various kinds of periodic movements, of the 

 twining of tendrils and climbing plants, and of movements 

 dependent on irritation, may be referred to a common prin- 

 ciple, and that in all these movements besides the elasticity of 

 the cell-walls the still unknown qualities of the protoplasm play 

 the most important part, and that consequently the ' streamings ' 

 of the protoplasm, the movements of swarm-spores and similar 

 occurrences must be ranked with these phytodynamical phe- 

 nomena. From this point of view phytodynamics would 

 appear to be one of the most important foundations of veget- 

 able physiology. The recognition of this fact is however of 

 very recent date, and to imagine that such a conception of the 

 movements of plants was present to the minds of the early 

 physiologists would be to attribute to the past ideas to which 

 it was entirely a stranger. These movements were scarcely 

 noticed even as curiosities in former ages, and it was not till 

 the end of the iyth century that some attention began to be 

 paid to them ; and very slow progress was made at a later time 

 in disentangling the relations which come under consideration 

 and which are some of them very complicated, in determining 

 the dependence of the phenomena on external influences, and 

 explaining to some extent their mechanical conditions. 



Single movements of parts of plants are noticed in a cursory 

 manner by some early writers. Varro was the first who men- 



