66 



Rhodora [April 



culties, which are especially apt to be shown by annuals, namely 

 those which arise from the very unequal nourishment of the different 

 individuals. This especially affects a group of plants which, while 

 quite ready to luxuriate in the best of soil, are equally capable of a 

 hardy advance into the packed earth of foot-paths or sterile sands, 

 where they suffer every degree of inanition. Crowding also affects 

 their manner of growth; thus the typical P. aviculare is normally a 

 prostrate plant, but when crowded the individuals are often perfectly 

 erect. Finally, the Polygonums of this section show a fondness for 

 brackish marshes and tidal Hats, where they become as one may say 

 maritimized, taking on very gradually the thicker leaves and more 

 fleshy character so common in halophytes. It is easy to see, there- 

 fore, why these species are confused in most herbaria. 



In interpreting the maritime forms I have been especially assisted 

 by Mr. W. P. Rich, who has devoted much attention to the group 

 and brought together an interesting suite of specimens. I am also 

 indebted to Prof. N. L. Britton and Dr. J. K. Small for the privilege 

 of examining and discussing with them many specimens in the 

 herbarium of the New York Botanical Garden, and to Mr. F. V. 

 Coville and Dr. J. N. Rose for the loan of many sheets from the 

 government collections at Washington. I have been kindly per- 

 mitted to examine also the Polygonums in the herbaria of Brown 

 University (including the recently acquired herbarium of Prof. W. 

 W. Bailey), the University of Vermont, and Middlebury College, and 

 in the private collections of Dr. E. H. Eames and Messrs. Walter 

 Deane, E. F. Williams, E. L. Rand, and J. F. Collins. Plate 35, 

 illustrating nearly all the forms here discussed, has been drawn with 

 great care by Mr. F. Schuyler Matthews. 



The section Avicuhiria, Meisn. Prodr. Gen. Polyg. 43> 8 5> is 

 characterized by incumbent cotyledons, triquetrous achenes, axillary 

 flowers, and 2-parted or 2-lobed stipules. None of these characters 

 separates the section sharply from other groups in the genus, but in 

 the case of our own northeastern species there never need be doubt 

 in recognizing the section, the axillary flowers alone being a sufficient 

 guide, except in P. arenarium, found only once on our coast. 



* Achenes at maturity conspicuously exserted beyond the inclosing calyx. 

 4. Prostrate, maritime ; achenes broadly ovate ; flowers relatively large, 

 2 to 4 mm. in length. 



P. maritimum, L. Foliage very pale and glaucous, often nearly 

 white: leaves of the branches small, narrowly oblong, very thick, 



