2 
been harvested (arranging them in approximate order of abun- 
dance): Syntherisma sanguinalis, Jacquemontia tamnifolia, Hete- 
rotheca subaxillaris, Richardia scabra, Cenchrus echinatus, Iso- 
pappus divaricatus, Cassia Tora. These were merely jotted 
down in walking along a road, with no attempt at completeness; 
and more prolonged observations over a larger area would of 
course disclose many more. One perennial that is commonly 
found in southern fields the same year they are cultivated, 
and was seen along roadsides at this time and place, is the 
nut-grass, Cyperus rotundus. It is able to exist in cultivated 
fields because it is propagated by corms and runners far enough 
below the surface to escape shallow plowing. 
No special search was made for old fields at this time, but 
the following plants seen along roadsides in the immediate vicin- 
ity are also common in fields that have lain idle for a few years: 
Prunus angustifolia, Rubus cuneifolius, Andropogon scoparius, 
Lespedeza striata, Capriola Dactylon, Cyperus rotundus, Eupa- 
torium compositifolium, Andropogon argyraeus. (There were also 
a few others which seem to prefer roadsides to old fields.) This 
list, which could also be greatly extended, includes two shrubs, 
and most of the herbs are perennial. In old fields nearly through- 
out the eastern United States, Andropogon scoparius, a native 
perennial grass, is one of the commonest weeds, and it com- 
monly grows densely enough so that fire can sweep through it, 
and if burned often enough the invasion of trees sensitive to fire 
may be long delayed. 
‘It is probably a belief widely held, if not often expressed, 
that if the human race should disappear from the earth or any 
considerable portion thereof, the original vegetation, consisting 
of species perfectly adapted to the soil, climate, etc., would re- 
store itself pretty well in a century or two, and the foreign in- 
vaders would be suppressed. 
The great majority of weeds prefer open situations, 50 that 
trees would tend to destroy them by shading them. Another 
factor that helps native plants in competing with exotics, €S- 
pecially in the southeastern United States, is fire. The long-leaf 
pine forests have undoubtedly been subject for ages to fires 0 
almost yearly occurrence, while other types of forest in the same 
part of the country have been burned over at less frequent inter 
vals.? Most of our weeds, as well as cultivated plants, come from 
* See Pop. Sci. Monthly 85: 338-361, October, 1914. 
