450 BicKNELL : Ferns and flowering plants of Nantucket 



J 



below. In a frequent state of the plant the ochreae become 

 enlarged and imbricated towards the ends of the branches and 

 of a reddish or bright purple color, the leaves remahihig very 

 small or even wholly undeveloped. In saline mud the plant is 

 sometimes deep bluish-green In color, and the leaves and joints of 

 the stem are somewhat succulent; such plants often become 

 much blackened in drying. In drier sandy soil it is erect and 

 paler green, often very slender and only sparingly branched. This 

 is the prevailing form on Nantucket, although the thicker-leaved and 

 Avidely branched bluish-green form also occurs. 



The normal achene of Polygonum prolijicum is about 2 mm. 

 long, ovoid, light brown, somewhat dull, minutely punctate, with 

 hard bony walls, and wholly included. Late in the season the 

 plant commonly produces manyachenes which become lanceolate 

 and conspicuously exserted and 3-3. 5 mm. long. These elongated 

 achenes differ further from the normal in being olivaceous and 

 shining with membranous walls. These profound modifications 

 result from the premature germination of the embryo which, while 

 still wholly enclosed, will be found to be bright green and purplish 

 in color and with elongating radicle. 



The elongated achene of Polygonuvi exsertum Small is of pre- 

 cisely the character of that of P. prolifiann and I am unable to 

 see that P, exsertnm is anything more than a semiviviparous state 

 of Polygonum rainosisshnnm Michx. In this species and in its 

 eastern representative, as well as in P, prolijicum^ both kinds of 

 achenes frequently occur on the same plant. This is also true of 

 Polygonvni Fowleri Robinson, and P, biixiforme and other species 

 occasionally develop similar achenes with viviparous tendency. 



Polygonum atlanticum (Robinson) comb. nov. 



P. ramosisswmin Michx. forma atlanticum Robinson, Rhodora 

 4: 72. 1902. 



Occurs rather sparingly on the borders of salt marshes and 

 along brackish tidal creeks : Acquidness Point, nearly three feet 

 in height; Quaise; near Pocomo Head; Little Neck. Observed 

 in full flower from before the middle of August until late in 

 September. 



Professor Robinson in distinguishing our coastwise representa- 



