The Phyllodes of Oxypolis filiformis, a Swamp Xerophyte* 



P>v KosiNA J. Rennert 



A large number of species of higher plants which live in ponds, 

 marshes and other extremely moist habitats present structural 

 characters of a xerophytic nature which have been most difficult 

 of interpretation. A special study of the phyllodes of Oxypolis 

 filiforviis t was undertaken by the author in the hope that some 

 additional light might be thrown on the subject. This work was 

 carried on in the New York Botanical Garden under the direction 

 of Dr. D. T. MacDougal, to whom I am indebted for valuable 

 advice and fruitful suggestions. 



Oxypolis filiforviis is an umbcllifer which grows in swamps and 

 along the borders of ponds in the southeastern United States, as 

 far north as Delaware. The leaves exhibit curious modifications 

 by which they depart widely from the uniformly broad or widely 

 dissected umbelliferous type, being reduced to stiff grayish-green 

 awl-shaped phyllodes, which have a structure as if made up of a 

 number of sections of varying lengths, the joints being distinctly 

 noticeable and marking the position of peculiar septa in the interior 

 tissues. This habit of the leaves gives the plant a rush-like ap- 

 pearance, an effect which is heightened by the small size of the 

 cauline, and the strong development of the basal phyllodes. The 

 entire phyllode is flattened along one side. A minute pit is to be 

 observed externally to every septum, occurring in the middle oi 

 the slightly flattened surface. 



Briquet % has given a detailed account of the results of his ex- 

 amination of this plant with respect to the anatomy of the phyl- 

 lodes. He describes the epidermis as a single layer of cells with 

 curved outer walls protected by a thickened outer membrane and 

 a folded cuticle. The stomata were noted as either flush with the 



* Read before the Botanical Society of America, by invitation, at Pittsburg, Pa. , 

 July I, 1902. 



f Oxypolis filiformis (Walt.) Britton. Tiedeniannia teretifolia (Muhl. ) DC. 

 ' \ Briquet, J. Etude de la feuille du Tiedmannia teretifolia J)C. Bull. Herb 

 Boiss. 5 : 461-465. 1897. 



403 



