2 INTRODUCTION 



that the protoplasm was the living part of the cell, and the seat of active 

 movement. Dutrochet l observed the influence of acids, alkalies, alkaloids, 

 saline and sugary solutions, temperature, light, oxygen and mechanical 

 stimuli on streaming in Chara fragilis^ while the influence of electrical 

 stimuli was investigated by Dutrochet and Becquerel (loc. cit, p. 80). These 

 empirical studies form the basis of our present knowledge of the influence 

 of stimuli on streaming movements, and though elementary in scope are 

 extremely exact. Schleiden 2 and Hassal 3 observed that rotation is not 

 confined to the cell-sap, but is most obvious in the outer denser granular 

 layers (of endoplasm) or in the 'mucus' bridles crossing the 'cell. It was 

 not, however, until Von Mohl had established the -fact that the protoplasm 

 forms the essential living substance of all plant (and animal) cells that 

 Schacht 4 showed the seat of the active movement to be in the protoplasm, 

 and concluded that it was merely an outward and visible sign of the vital 

 activity of the latter. Von Mohl studied the same phenomenon, and deter- 

 mined the velocity of streaming between 15 and 16 R. in a variety of 

 plants 5 . He concluded that the nucleus exercised little or no influence, 

 and that the chloroplastids played a directly active part in inducing 

 streaming, but gave up this view later 6 . 



Nageli 7 in 1860 investigated more exactly the relation between stream- 

 ing and temperature, and showed that a geometric proportionality existed 

 between the increments of temperature and of velocity. Both Nageli and 

 Pringsheim 8 held that the force inducing movement had its origin between 

 the cell-sap and the lining layer of protoplasm, a theory which Berthold 

 still upholds, but one to which considerable doubt attaches. 



Kiihne established the necessity of a supply of oxygen for the move- 

 ment, and indeed concluded that contact with oxygen formed the necessary 

 essential stimulus to protoplasmic movements of all kinds 9 . 



My own observations, however, showed that streaming might continue 

 in certain cases for prolonged periods of time in the absence of oxygen, and 

 these observations have subsequently been confirmed by Kuhne himself, 

 and in part also by Ritter 10 . 



Ann. sci. nat., 1838, ii. sen, T. IX, pp. 5, 65, 

 Principles of Botany (Eng. Trans.), 1849, p. 92, 

 British Freshwater Algae, I, p. 85. 

 Die Pflanzenzelle, 1852, p. 340. 

 Von Mohl, Bot. Zeitg., 1846, p. 73. 

 Vegetable Cell, 1852, p. 39 (Eng. ed.). 

 Beitrage zur wiss. Botanik, 1860, u, p. 62. 



Nageli u. Schwendener, Das Mikroscop, p. 399 ; Pringsheim, Unters. iiber den Bau und die 

 Bildung der Pflanzenzelle, Berlin, 1854, p. 9. 



9 Kiihne, Unters. iiber das Protoplasma und die Contractilitat, 1864, p. 105. 



10 Ewart, On Assim. Inhib., Journ. Linn. Soc., 1895, Vol. xxxi, p. 42; N. Kiihiie, Zeitschr. 

 f. Biol., 1897, Bd. xxxv, pp. 43-67; 1898, Bd. xxxvi, pp. 1-98; G. Ritter, Flora, 1899, LXXXVI, 

 pp. 329-60. 



