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manner of the sphagnum. Along most of the stem these branch 

 clusters are scattered, but toward the tip they usually grow so 

 close together as to form a rather compact rosette which some- 

 times is mistaken for a flower. It might be added that the bran- 

 ches in each cluster are of two sorts: one kind stands out at right 

 angles to the main axis ; the other kind droops down alongside the 

 stem and forms a sort of loose, spongy matting around it. 



And not only is the arrangement of the branches on the stem 

 distinctive. Quite as striking is the arrangement of the leaves 

 on the branches. Every branch is completely covered over by a 

 series of tiny, more or less spoon-shaped leaves, which closely 

 overlap one another, somewhat after the manner of shingles on 

 the roof of a house. 



To ivhat structural peculiarities does the sphagnum owe its 

 efficiency as an absorbent? 



To a limited degree certain of the features already described 

 adapt the sphagnum to absorb liquids: the close overlapping of 

 the leaves around the branches, and the sponge-like matting of 

 the pendent branches around the stem. But the real secret of 

 the sphagnum's efficiency as an absorbent lies in the remarkable 

 microscopic structure of its leaves. 



Before discussing the somewhat complicated sphagnum leaf, 

 I will describe briefly the much simpler structure of an ordinary 

 moss leaf, as it looks under the microscope. Such a leaf consists 

 of a single layer of tiny microscopic cells. Seen in surface view 

 the individual cells are polygonal in outline, but in reality, con- 

 sidered as solids, they are prismatic in shape. All of the cells in 

 the leaf are essentially similar to one another: without exception 

 they are green and living and they are all of approximately the 

 same size and shape. 



But in a sphagnum leaf the structure is much more complex. 

 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 



