226 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



But in a sphagnum leaf (fig. 1) the structure is much more com- 

 plex. Here also there is just a single layer of cells, but these cells 

 are of two totally different kinds. First, as in the ordinary moss 

 leaf, there are the green, living cells. But these green cells, in the 

 sphagnum leaf, are very small and very much elongated, and they 

 are arranged to form a sort of open network which runs all through 

 the leaf. In the meshes of this network occurs the second kind of 

 cell. These cells are large, without color, dead, and perfectly empty. 

 It is to the presence of these large, colorless cells and to their remark- 



A SIMPLE MOSS LEAT 



3Lock Section of 

 Portion or Leaf 



Surface 

 View of 

 Entire 



Leaf 



A SPHAGNUM LEAF 



Block Section of 

 Portion of Leaf 



Surface 

 View of 

 Entire 



Leaf 



Fig. 1. 



able structure, which I shall describe next, that the sphagnum owes 

 its wonderful power to take up liquids. 



Now, to a certain extent, the cells of any moss leaf are able to 

 absorb liquids; but the ability of the ordinary green cells in this 

 respect is insignificant when compared with that of the large, color- 

 less cells of the sphagnum leaf. These, because of their capacity for 

 absorption, may well be referred to as the absorbing cells. There 

 are two features in these cells which especially adapt them to the 

 function of absorption: First, the wall of each and every one of 



