554 History of the Doctrine of [BOOK in. 



and movements of irritability were connected without difficulty 

 with the forms of movement that had been long known in the 

 vegetable kingdom, and contributed to correct the views that 

 had been entertained respecting them. But this was not the 

 case for a time with two phenomena which also fall within 

 the province of phytodynamics, namely normal growth and the 

 movements of the protoplasm, which exhibit the two opposite 

 extremes, so to speak, of the facts connected with movement. 

 Various measurements had been made of the growth of plants 

 since the beginning of the century, and attempts had been 

 made to establish its dependence on light and heat, but with- 

 out any great success. Treviranus had rediscovered the move- 

 ments of the protoplasm in 1811 in Nitella. Similar move- 

 ments were repeatedly pointed out by Amici, Meyen, and 

 Schleiden in the cells of higher plants, but they were taken for 

 streamings of the cell-sap ; it was still unknown that all these 

 were movements of the same organised substance, which moves 

 independently in water in the form of swarmspores. These 

 phenomena, especially the movements of swarmspores, were 

 noticed and studied separately between 1830 and 1840, but no 

 one thought of bringing both these movements and the me- 

 chanical laws of normal growth into connection with the 

 phenomena which had usually been treated together under the 

 head of movements in the vegetable kingdom. De Candolle 

 and Meyen did not mention them in this connection in their 

 'Compendia' of 1835 and 1839; Meyen on the contrary 

 discussed the 'circulation of the cell-juice' with nutrition, and 

 the movement of swarmspores with the propagation of Algae. 

 The two writers just named, like Du Hamel before them, 

 divided into two main groups the movements in the vegetable 

 kingdom which had been long known and were usually put 

 together, and treated of geotropic and heliotropic curvatures 

 and the movements of tendrils and climbing-plants under the 

 head of direction of plants, and the periodical movements and 

 movements connected with irritability under that of move- 



