ISO 



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.-^ 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. 



