376 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



carrollata, Rhus toxicodendron^, Oenothera biennis, Oeothera 



serrulata, Ceanothus americanus, Eryngimn yuccaefolium, As- 



clepias syriaca, Convolvulus sepiuni. 



Plants characteristic of tlie permanent prairie, such as Soli- 

 dago and Lespedeza, were found most frequently near the edg'e 

 of the uncultivated prairie strip. In the center of the cultivated 

 area in the upturned earth around an animal's den were Cirsmm 

 lamceolatum, CJienopodium (dbuni, Heliantlius grosseserratus, 

 Xanthium canadense, Monarda fistulosa and Lactuca canadensis. 

 The patch uncultivated for twenty-one years indicated that its 

 flora was undergoino; succession changes. It contained almost 



Fig. 151. — Fenced patch of prairie. Alluvial basin. 



twice as many species as either of the other two areas, including 

 species of l)oth the newer and older associations. 



Reversions fi'om ruderal to ])rairie type after removal of the 

 criginal i)rairie phints is relatively rare in this cool, relatively 

 dry, wind swept region as coiH]>ared with ;i moistcr, warmer 

 climate.* This reversion is sometimes seen in the upland in this 



*Near Houston. Texas, was otaserved an abandoned rice field located sligbtly 

 above the level of a cypress swamp and bordered on two sides by forests 

 of Pinus taeda, on one by a road and on the other by a pasture. The field 

 was too low for the successful growing of rice, which must be kept wet only 

 a portion of the year and then dried toward harvest time. After no culti- 

 vation for six years, this field had acquired the usual aspect of the prairie 

 of that region and was being ra-pidly invaded by seedling trees of P. taeda, 

 many of which were three or four feet high. Such a transition is not un- 

 common in this ■v\^'^rm, moist climate. 



In the .same vicinity along the San Jacinto river a forest of Pinus taeda 

 with large trees was growing on land which had forty years earlier been 

 cultivated for crops. 



