8 MEMOIRS FROM THE DEPARTMENT OF BOTANY OF COLUMBIA COLLEGE, 
GEOGRAPHIC DISTRIBUTION. 
The genus as a whole has a wide distribution, ranging from the tropics to the polar 
regions, and from the level of the sea to the highest altitudes at which flowering plants 
can withstand the rigorous environment characteristic of such regions. 
The genus divides itself into a number of very natural sections, and we notice a char- 
acteristic distribution by subgenera. Thus Bistorta is typically aretic, while Aconogonon 
is normally alpine. The subgenus Tiniaria is north temperate in its distribution, Duravia 
is Californian, Tephis is South African, and Cephalophilon is confined to southern Asia. 
Other sections as Persicaria, Avicularia, Amblygonon and Echinocaulon are tropical, tem- 
perate and arctic in their range. 
There are probably some two hundred and fifty living species ; of these about ninety 
occur in the western and one hundred and sixty in the eastern hemisphere. Seventy are 
now known to exist in North America, and about thirty species are recorded for South 
America, and there are forty-two peculiar to the former region, while only fifteen are at 
the present time known to be endemie in the latter. 
THE GENERAL MORPHOLOGY. 
During the latter part of this century the genus has been accepted in about the same 
way that Linnaeus understood it when he wrote the Species Plantarum. His contem- 
poraries, however, and the botanists for some years after his time, held quite different 
views as to its limits. At one time or another the genus as we now understand it has been 
divided into as many as eight or ten genera. Adanson,' for instance, founded a genus 
Tephis on a South African plant. The Polygonum of Tournefort was represented by those 
plants which Meisner included under his section Avicularia and which were embraced by 
the genus Centinodia of J. Bauhin.* A second genus of Tournefort was Persicaria, which 
is about the same as Adanson’s later Tovara* and Rafinesque’s Antenoron.? Loureiro de- 
scribed a genus Lagunea,® which is the same as Meisner’s section Amblygonon, and a third 
genus of Tournefort was Bistorta, which has also fallen to subgeneric rank. Chylocalyx of 
Hasskarl,’ now standing as subgenus Echinocaulon of Meisner, and the latter’s Tiniaria, 
representing Dumortier’s Bilderdykia,* have stood at one time or another in generic rank. 
So Polygonum has had a varied history, but of late all these divisions have been 
brought under one generic head and retained there as sections or subgenera. Although 
commonly accepted in this way, there has been more or less discussion concerning the 
1Fam. Pl, 2: 276. 4Fam. Pl, 2: 276. 7 Beibl. 2 : 20. 
2Monog. 43 and 85, 5 Fl. Ludoy, 28 SFI. Belg. Prodr, 18. 
3 Hist, 3: 374, FW], Coch, 1: 271. 
