STRUCTURE AND DEVELOPMENT. 67 



found in his wonderful little book 6 Uber die Bichtungs- 

 verhaltnisseder SaftstromeindenZellen der Cliaraceen.' 



Numerous bodies are found imbedded in the stream 

 of moving protoplasm, consisting of nucleoli, starch- 

 granules of various sizes, loose chlorophyll-grains 

 and curious minute ciliated spheres. The rate of 

 progress of the cyclotic stream depends largely on the 

 temperature, as may be readily observed by warming a 

 slide on which a specimen has been placed. Sachs found 

 that the slowest continuous movement was when the 

 temperature of the water was 1 C., the most rapid 

 when it was 37 C C. ('Lect. Physiol. PI.,' Transl., p. 606). 



Almost ever since the publication of Corti's dis- 

 covery of cyclosis in 1774, its investigation has engaged 

 the attention of botanists, experiments having been 

 carried out with a view to ascertaining the causes and 

 nature of the cyclotic flow and the conditions affecting 

 it, and numerous memoirs have been published on 

 the subject so that the literature relating thereto is 

 considerable. The views put forward and the con- 

 clusions reached have been ably summarised by Pro- 

 fessor Ewart in his monograph ( On the Physics and 

 Physiology of Protoplasmic Streaming in Plants,' from 

 which exhaustive and painstaking work the follow- 

 ing particulars are taken. 



It is shown that an increase of temperature, within 

 certain limits, by causing a decrease in the viscosity 

 of the moving protoplasm, accelerates its flow. In 

 the cell of a Nitella the times taken to cover a space 

 of 1 mm. at 18 C., 27 C., and 45 C. were 54, 38, 

 and 25 seconds respectively. 



Streaming appears to cease permanently when the cell 

 is exposed to as low a temperature as -5 C., and on 

 continued exposure to as high a temperature as 45 C. 



