INTRODUCTION. 
The genus Polygonum is the type of the natural family PoLyGonacrar. This 
family of dicotyledonous spermatophyta has no very close affinity to other groups, and 
authors do not differ, to any great degree, as to the relative position of the family. 
Among the writers who have arranged groups in a linear sequence, Meisner’ placed 
the PoLyGonaceAr between PETIVERTACEAE and ErtoGoNEAE; Endlicher*? brought them 
in between AMARANTHACEAE and NycTaGINneaE, Bentham and Hooker* between the 
Batipear and the PoposromaceaAr. Lately Greene* has placed the family between 
ILLECEBREAE and NycraGrneagz. These different groupings are practically the same and 
logical as far as the system permits. Baillon,° of all the writers on genera, seems to have 
made the most illogical disposition of the family in placing it between PLUMBAGINACEAE 
and JuGiANDACEAE. On the other hand, Engler and Prantl,’ working out their system 
on the divergent lines of the descent of groups, place PoLyGonacrar at the beginning 
of one of their lines, and follow with the family Cuenopopracrar. The limits of the 
family have with few exceptions been accepted in about the same way. Dumortier,’ in 
1829, transferred the genus Eriogonwm to the CHENoPopIACEAE, making it there the type 
of a tribe. Meisner* some years later removed the genus from that family and raised it 
to ordinal rank, founding a family on it as a type, and including under it the poly- 
gonaceous genera Pterostegia, Mucronea and Chorizanthe. 
The family as understood by me embraces some seven hundred species, which fall 
into about thirty-five natural genera, some of which are monotypic, while others include 
numerous species. It is distributed throughout the globe, being well represented in the 
tropical, the temperate and the arctic regions. The greater number of species occur, how- 
ever, in the Northern Hemisphere. There are a few interesting points concerning the 
geographical distribution of the genera. In the first place, there are those with a re- 
stricted area of distribution and others which are general throughout. We find Macounia 
(Koenigia L., not Adans.) confined to a cireumboreal zone and to the higher parts of the 
Himalayas with a corresponding temperature, while such genera as Coccoloba, Symmeria 
1Pl. Vas. Gen. 228. ‘Fl, Francis, 132. 7Anal. Fam. 17. 
2Gen. Pl. 304, 5 Hist. des. Pl. 367. 8Pl. Vas. Gen. 229. 
3Gen. Pl. 3: 88. ®Nat. Pfl. Fam. 3: Abt. 1a, 1. 
