4 



BiCKNELL : Ferns and flowering plants of Nantucket 443 



the geographical, ecological, and organic relations of these units 

 depends in a measure on this matter of names and will scarcely be 

 assisted by that timorous method in taxonomy which abandons its 

 species at the least evidence of intergradation, however obscure or 

 exceptional the case may be. 



In our present imperfect knowledge of this group I have re- 

 frained from treating as a species any of its members for which 

 a published specific name was not found to be available. 



As Polygonum aviciclarel^. occurs on Nantucket in grassy places 

 along the streets and here and there at outlying points, it is a dull 

 bluish-green plant, ascending or erect, slenderly branched from the 

 base, the leaves neither crowded nor greatly reduced in size on the 

 ultimate branches, rather thin, often only obscurely veined, oblong- 

 lanceolate, acute or obtusely pointed, distinctly petioled; ochreae 

 thin-membranous, at first silvery white and acute, becoming pale 

 brown and more or less shriveled-lacerate ; flowers distinctly ped- 

 icelled ; mature flowering calyx 2-2.5 ^*^' ^^^g^ margined with 

 w^hite or purplish ; achene 2—2.5 mm. long, 1.5 mm. thick, unevenly 

 trigonous, the broader faces ovate, nearly plane, dark, dull, rugu- 



lose-striate. 



A slender often erect form, found m grassy plots on shady 



r 



streets, seems to answer the description of var. agrarhim Koch. 



There is a form of this plant that appears to be well enti- 

 tled to recognition which was not found on Nantucket, being 

 apparently more common northward or at higher elevations. It 

 is characterized by slender elongated branches, straggling or pros- 

 trate habit, and very pale color ; the leaves, which are sometimes 

 almost whitened beneath, are rather small, well separated, oblong 

 or somewhat spatulate, mostly rounded or obtuse at the apex, and, 

 except the midvein, nerveless or nearly so ; stems usually flor- 

 iferous in all the axils ; calyx margined with white or clear pink. 

 It is perhaps the Polygonum avictdare var. diffiisum of Meisner. 



* Polygonum monspeliense Thieb. in Pers. Syn. i : 439. 1805. 



?P. aviculare var. vegctum Ledeb. FL Ross. 3: 532. 1849. 



Found only \n the neighborhood of the town, occurring \r\ 

 sandy places, or in pure sand, near the shore. This was the only 

 Polygonuui found in flower in June, being in full bloom and with 

 mature fruit as early as June 20. 



