424 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



rather the beofinninfr of a new succession resulting from the 

 break-up of an old one. 



It mig'ht be interesting to follow the fortunes of this new suc- 

 cession, but the changed occupation of the writer prevents. 

 Moreover, it is a bit discouraging to trace the changing dynasties 

 in a kingdom where rivals for supremacy are so interested in 

 securing a "place in the sun" that they neglect the important 

 matter of securing a place in the earth, and let the very ground 

 crumble under their feet as they struggle with each other. A 

 few short notes on conditions during the season of 1917 will 

 therefore serve the present purpose, and bring the series to a 

 close. 



It was noted above that most of the southwestern end of the 

 levee disappeared and was replaced with new material. This 

 was in part earth, but mostly garbage and manure from the city, 

 and the vegetation here was therefore extraneous and unnatural. 

 Mushrooms were very plentiful, most conspicuous being two or 

 three species of Coprinus. In several patc'hea there were thick 

 stands of watermelon seedlings, and elsewhere scattering plants 

 of field corn. The dominant in this "artificial" vegetation was 

 common oats. 



In the third paper of this series mention was made of a 

 portion of the levee which was regraded in the spring of 1916, 

 and on w^hieh a stand of Amaranthus reiroflexus, the dominant 

 of the first season, made its appearance again as dominant. Dur- 

 ing the season of 1917, while the succession was not nearly so 

 sharply marked nor the replacement nearly so complete as was 

 the case with the original cycle, the pigweed was again driven 

 out by its old rival, Chenopodium album. 



The rest of the levee had been almost completely regraded, 

 and here everything was ch?/>s and anarchy. In only one place 

 was there any trace of the old succession. Here patches of 

 wild lettuce alternated with horse weed, Erigeroii canadensis, 

 which was evidently in the process of crowding out the lettuce 

 just as the latter had crowded out the goosefoot. The invasion 

 made by the tall ragweed during the earlier seasons was pretty 

 completely wiped out by the grading operations and the weed 

 driven back to its original terrain. 



For the rest, the vegetation was rather a hodge-podge, con- 

 sisting mostly of Amaranthus retroflexus, Chenopodium album 

 and Abutilon theophrasti, the plants being mixed together indis- 



