The few sentences in the autobiographical chapter give with sufficient clearness the connection between the ‘Power of Movement,’ and one of the author's earlier books, that on ‘Climbing Plants.’ The central idea of the book is that the movements of plants in relation to light, gravitation, &c., are modifications of a spontaneous tendency to revolve or circumnutate, which is widely inherent in the growing parts of plants. This conception has not been generally adopted, and has not taken a place among the canons of orthodox physiology. The book has been treated by Professor Sachs with a few words of professorial contempt; and by Professor Wiesner it has been honoured by careful and generously expressed criticism.

Mr. Thiselton Dyer has well said: “Whether this masterly conception of the unity of what has hitherto seemed a chaos of unrelated phenomena will be sustained, time alone will show. But no one can doubt the importance of what Mr. Darwin has done, in showing that for the future the phenomena of plant movement can and indeed must be studied from a single point of view.”

The work was begun in the summer of 1877, after the publication of ‘Different Forms of Flowers,’ and by the autumn his enthusiasm for the subject was thoroughly established, and he wrote to Mr. Dyer: “I am all on fire at the work.”