INTKODUCTION. 3 



creased growth, first on one side and then on another, 

 is a secondary effect, and that the increased tur- 

 gescence of the cells, together with the extensibility 

 of their walls, is the primary cause of the movement of 

 circumnutation.* 



In the course of the present volume it will be shown 

 that apparently every growing part of every plant is 

 continually circumnutating, though often on a small 

 scale. Even the stems of seedlings before they have 

 broken through the ground, as well as their buried 

 radicles, circum nutate, as far as the pressure of the 

 surrounding earth permits. In this universally pre- 

 sent movement we have the basis or groundwork for 

 the acquirement, according to the requirements of the 

 plant, of the most diversified movements. Thus, the 

 great sweeps made by the stems of twining plants, 

 and by the tendrils of other climbers, result from 

 a mere increase in the amplitude of the ordinary 

 movement of circumnutation. The position which 

 young leaves and other organs ultimately assume 

 is acquired by the circumnutating movement being 

 increased in some one direction. The leaves of 

 various plants are said to sleep at night, and it will 

 be seen that their blades then assume a vertical 

 position through modified circumnutation, in order 

 to protect their upper surfaces from being chilled 

 through radiation. The movements of various organs 

 to the light, which are so general throughout the 

 vegetable kingdom, and occasionally from the light, 

 or transversely with respect to it, are all modified 



* See Mr. Vine's excellent dis- Naturkunde in Wiirtemberg,' 

 cussion (' Arbeitcn des Bot. Insti- 1874, p. 211) on the curious move- 

 tuts in Wiirzburg,' B. II. pp. 142, ments of Spirogyra, a plant con- 

 143, 1878) on this intricate subject. sisting of a single row of cells,.aro 

 Hofmeister's observations (* Jah- valuable in relation to this subject, 

 reschrifte des Vereins fur Vaterl. 



