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leaves may be described in this connection, namely, Le- 

 dum latifolium Ait. The under surface of the leaf has 

 small half-spherical projections or elevations on which 

 the raised stomata occur. Here are three distinct features 

 aiding transpiration : First, the extremely large air spaces 

 existing in these elevations; Second, the projections 

 themselves which serve to increase the surface covered 

 with stomata and also aid in throwing these higher; 

 Third, the raised stomata. On the other hand,' tran- 

 spiration is retarded by the filz formed by the long hair 

 cells which grow close together through the central por- 

 tion of the leaf but more scattered toward the edges, 

 here the lack of hair is supplied by the edges rolling 

 under. Thus again is formed a protected cavity where 

 the moisture passing from the stomata may be retained. 

 These are, in brief, the conditions under which this 

 form of stoma was found in the plants studied. Its 

 constancy of occurrence under similar conditions suggests 

 some definite advantage thus secured to the plant, but 

 these conditions are too complicated to admit of the 

 simple solution suggested in case of the tropical ferns. 

 With these every thing points to the one conclusion ; the 

 supply of water in the soil is abundant throughout the 

 entire year either through frequent rains or its equi- 

 valent of moisture in the air; the ferns are known to 

 grow rapidly, acquire great size and to be extremely 

 sensitive to a lessening of the amount of moisture in the 

 air surrounding them. The conclusion is a very natural 

 one, that the principal object of the raised stomata, is 

 to counteract the hindrance which the heavy moist air 

 offers to a free and rapid passage of water through the 

 plant. If we compare these circumstances with those 



