HISTORICAL 5 



a plant is injured, respiration becomes after a time more active near the 

 wounded area, and at the same time a slight rise of temperature occurs. 

 This effect also slowly radiates a slight distance from the injury, but the 

 appearance of streaming precedes the maximum increase in respiratory 

 activity, and therefore simply heralds and perhaps aids in the subsequent 

 marked increase of katabolism instead of being caused by it. Streaming 

 does not always ensue as the result of injury, and hence its occasional 

 appearance is more probably due to a diminution in the resistance to flow 

 permitting a pre-existent tendency to streaming to become externally 

 manifest, than to an actual induction of this tendency as the result of 

 injury. 



The conditions determining the flow of liquids through capillary tubes 

 were first investigated by Poiseuille *, who established a formula expressing 

 the relationship of these conditions and also endeavoured to trace the 

 influence of different dissolved substances upon the movement of the blood 

 in the blood-capillaries. In the case of plant-cells, however, the flow is in 

 closed tubes, and takes place in opposite directions on the two sides of the 

 capillary, none of the moving fluid escaping from either end (cf. Fig. 5, 

 P- 38). 



1 M6n. des Sav. fitrang., 1846, ix, p. 433. 



