PIONEER PLANTS ON A NEW LEVEE. III. 
FRANK E. A. THONE. 
The present paper is the third of a series of brief notes on 
the yearly changes in the re-vegetation of a soil area exposed 
by the building of a new levee in Des Moines in the spring of 
1914. 1 
In the first paper the general character of the plant pioneers 
during the season of 1914 was discussed/ with speculations as 
to their probable modes of travel. In the second, note was made 
of the replacement of the first year ’s dominating plant, Amaran- 
thus retroflexiis, by Chenopodium album, which gained the 
leadership through its earlier germination, and of the threatened 
overthrow of the latter by Lactuca scariola. 
The writer regrets that the hasty survey lie was able to give 
the place during the past summer (1916), together with his in- 
ability to visit it at all during the present spring, do not make 
possible anything like a comprehensive summary of conditions 
now prevailing on this strip of ground. However, one or two 
of the more marked changes seem to be worth recording. 
In the first place, the statement made in the spring of 1916 
that the goosefoot would probably hold its place as dominant 
that summer, but have to fight for it with the wdld lettuce the 
following year, proved to be too conservative. 
The lettuce was overwhelmingly the dominant, crowding the 
goosefoot practically to extinction, just as the latter had in its 
day crowded the pigweed. It was also holding its own against 
the invasion of Ambrosia trifida, which during the two previous 
seasons had been spreading up the levee from its original re- 
stricted territory on the lower end. The two previous domi- 
nants had failed to prevent this weed from encroaching on 
their territory. Scattered among the wild lettuce was a good 
deal of Erigeron canadense, which formed dense clumps here 
and there. This plant was a newcomer, having appeared for 
the first time during the preceding season. It may. possibly be- 
come a contender for first place. 
Proceedings Iowa Academy of Science, Vol. XXII, pp. 135-142, and Vol 
XXIII, pp. 423-426. 
