194 STRUCTURE AND LIFE HISTORIES 
ness from four cells in the main stem, to one or two cells 
in the smaller branches. The leaves are only one cell thick, 
and are densely crowded on the stem, having, at maturity, 
what is known as the two-fifths arrangement; that is, 
if one starts with a given leaf and follows upward in a 
spiral around the stem, he will pass five leaves before he 
comes to one vertically above that with which he started, 
FIG. 139. Sphagnum sp. Upper portions of leafy plants, showing 
sporogonia. 
and in doing this he will have passed twice around the 
stem. The leaves of sphagnum never have a mid-rib 
or other veins, and correlated with this is the entire 
absence of any fibro- vascular bundles in the stem. This 
is one of the features that marks the plant as of lower 
organization than the fern. The stem forms numerous 
branches, usually one for every fourth leaf, and glandular 
hairs are usually met with at the bases of very young 
leaves (Figs. 140 and 141). 
