INFLUENCE OF ENVIEONMENT ON PLANTS 335 



surmounted, affording large reservoirs of air in the interior 

 of all parts that are submerged, so that the slow rate of 

 renewal of air does not impede the gaseous interchanges 

 which the protoplasts require. These intercellular reser- 

 voirs are not confined to the vertical stems, petioles and 

 leaves, but occur also in the more woody stems or rhizomes 

 which many of these plants possess (fig. 144). 



FIG. 144. SECTION or RHIZOME OF Marsilea. 

 co.la, lacunae in cortex. 



The absence of the transpiration current appears to be 

 correlated with a comparatively small development of the 

 plant-body. The large quantities of inorganic salts which 

 the dilute solutions absorbed by the roots carry into the 

 plant, in cases where the total absorption is very great 

 owing to a large transpiration, lead to a large increase of 

 constructive activity. In the absence of such an enormous 

 absorption the plant-body does not receive the materials 



