STRUCTURE AND LIFE HISTORIES 
illustrated than in the ferns. We shall therefore begin 
our study of life histories with that group of plants. 
141. Description of a Fern Plant. The more common 
ferns of temperate regions have underground stems or 
rhizomes (sometimes called root-stocks), so that only the 
FIG. 109. Tree ferns on the military road between Cayey and Caguas, 
Porto Rico. (Photo by M. A. Howe.) 
leaves appear above ground. 1 The stem may be branched 
or unbranched. When branched, the branches are pro- 
duced without reference to the insertion of the leaves, 
in contrast to the habit of higher plants of forming 
branches only in the upper angle (axil) between the stem 
1 The leaves of ferns are often called fronds. 
