CHAP, in.] the Movements of Plants. 559 



vegetable cells. A new substratum for the movements in 

 plants, and one of the simplest kind, was thus obtained ; and 

 Na'geli attempted in 1849 a mechanical explanation of the 

 movements of swarm-spores, while in 1859 De Bary exhibited 

 in the Myxomycetes most instructive examples of such move- 

 ments. If Na'geli failed in his attempt, yet it seemed possible 

 that the protoplasm had an important share in the production 

 of all phytodynamic phenomena, and the idea appeared 

 capable of a very wide application when Unger pointed out 

 in 1855 the resemblance between vegetable and animal pro- 

 toplasm. It is true that not one of these later observations 

 led to any conclusive results till after 1860 ; but that the whole 

 subject of phytodynamics had made considerable advance as 

 early as 1850 is apparent from the account given of it by 

 von Mohl in his 'Vegetabilische Zelle' of 1851, and by Unger 

 in his ' Lehrbuch der Anatomic und Physiologic der Pflanzen ' 

 of 1855. Von Mohl chiefly exposes the unsatisfactory nature of 

 the attempts that had been made to explain the phenomena ; 

 Unger, on the other hand, shows how much that is funda- 

 mentally important had been already established. 



The mechanics of growth had not been included by former 

 writers among the phenomena of phytodynamics, nor was it so 

 included by either Unger or von Mohl. It seemed to be sup- 

 posed that there was a fundamental difference between growth 

 and other movements in the vegetable kingdom, and this idea 

 was entertained even in the most recent times. From the time 

 of Mariotte and Hales no one had made the mechanical laws 

 of growth the subject of special investigation or theoretical 

 consideration ; yet some observations had been made on the 

 formal relations of growth and its dependence on external 

 influences. Ohlert (1837) was the first after Du Hamel who 

 studied the distribution of growth in the root ; Cotta in 1806, 

 Chr. F. Meyer in 1808, Cassini in 1821, Steinheil and others 

 made measurements in connection with the same question in 

 the stem, but only with the result of showing that the distribu- 



