61 



leaves as a permanent condition of their foliage. A cross sec- 

 tion of a leaf of Spartina stricta exhibits xeropnytic structiirf^. 

 although the plant lives in abundance of water. Water inhab- 

 iting plants showing this structure, such as rushes, sedges, 

 flags and the like, are as yet a puzzle to botanists. Just why a 



Figure 1. 



Diagrammatic cross section of a portion of leaf of Spartma 

 stricta showing grooves. 



species whose roots are in contact with abundant and peren- 

 nial water supply should show every evidence* of suffering 

 from drouth is still unloiown, but it is conjectured that the 

 water contains something in solutioii which is injurious to 

 vegetable tissue ; or else the reflection of the sun on the water 

 causes excessive heat and consequent rapid evaporation of 

 vv-ater from the leaf surface. Of the two, the former conjecture 

 seems the more likely, and it will be of interest to note that 

 Spartina stricta oft'ers some evidence in support of this theory. 



Stomata are located on the inner or ventral surface, and are 

 found only on the sides of the grooves. Their presence here is 

 evidently for protection, as, when the leaves are in a rolled con- 

 dition, the walls of the grooves approach, thus reducing the air 

 spaces between them, or obliterating them, in this condition 

 the mouths of the stomata are brought into contact with the op- 

 posite walls of the grooves instead of air spaces into which the 

 product of transpiration might be emptied. 



It is on the walls of the grooves that the salt-secreting cells 



(a) North American species of Spartina. 



(b) Flora of the Southeastern United States. 



(c) Flora of the Southern States. 



