INFUSION OF CARBON DIOXIDE 



19 



stomate varying from the atmospheric density, p, to a lower 

 density, p', at the stomate cut perpendicularly by the lines 

 of flow of carbon dioxide converging to the opening of the 

 stomate * (Fig. 1). Thus it is that the increased flow of gas 

 through the stomate is possible. 



The second section in the route of the carbon dioxide is 

 through the tube formed by the guard cells. Through this 

 tube the flow is inversely proportional to the length of the 

 tube, but the system of external shells increases the resistance 

 to the flow (Fig. 2). Finally, in the third section the tube 

 opens into the air-space system of the mesophyll bounded by 

 the absorbing surfaces of the chlorenchyma ; here the con- 



Fig. 2. 



verse of the first part of the path obtains, diffusion shells over 

 the lower opening of the stomate, where the density of the 

 carbon dioxide is p , being formed (Fig. 3). Thus in the whole 

 system there is a gradient of density from p to, say, o } with a 

 set of shells at both ends of the stomatal tube (Fig. 4). 



The obstruction to gaseous diffusion inseparable from a 

 multiperforate septum such as the stomatal epidermis of a 

 leaf, varies according to the distance apart of the perforations : 

 if they are placed at distances roughly equal to ten times the 

 diameter of a perforation, each will act independently without 

 interference by its neighbours and conform to the law of di- 

 ameters. When situated more closely together, it was found 



* Q = 2*0, + ,/)D. 



