Christensen, Carl. <br/><br/>
Index filicum :  supplementum tertium pro annis 1917-1933 / 
Carl Christensen. 
 - Hafniae :  H. Hagerup,  1934. 
 - 219 p. ;  25 cm. 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Ferns--Classification.