August, 1955 
Hedeoma hispida, R. aromatica, and Ger- 
ardia (possibly G. aspera). The 75-mil- 
acre unit minus the 10-milacre border 
strip contained 29 species. The 75-mil- 
acre unit contained 33 species. 
Frequency of Occurrence of Spe- 
cies.— The frequency, or repeated occur- 
rence, of plant species in Phegley and 
Sampson prairies was determined from 
species lists of each of the following plot 
sizes: 1/256-, 1/64-, 1/16-, 1/4-, and 
l-milacre. Although the 1/256-milacre 
unit was not marked in the field, data for 
plots of this size were obtained from maps 
of the mapped central milacre of both 
Sampson and Phegley prairies, figs. 8 and 
9. On such maps the northwest quarter 
Evers: Hitt Prairies or ILLINors 
389 
of the milacre was divided into 64 equal 
quadrats and, from these, species lists were 
compiled. The metric equivalent of this 
quadrat size is 0.0156 square meter. For 
any given plot size the frequency was ex- 
pressed as a percentage computed by divid- 
ing the number of quadrats in which the 
species occurred by the total number of 
quadrats of that size employed. 
Sampson Prairie—Table 10 summa- 
rizes the data for the frequency study in 
unpastured Sampson prairie. It is evi- 
dent that the 1/256-milacre size was too 
small for use in ecological studies of IIli- 
nois hill prairies; only one species, An- 
dropogon scoparius, attained a high per- 
centage of occurrence. The 1/64-milacre 
Table 11—Frequency of occurrence of plant species in plots of five sizes, Phegley hill 
prairie. 
Size A Size B Size C Size D Size E 
(1/256 (1/64 (1/16 (1/4 (1 
Mivacre, Mivacre, MILacre, MILacre, MILacre, 
0.0156 0.0625 0.25 1.01 4.05 
SQUARE SQUARE SQUARE SQUARE SQUARE 
SPECIES Meter) Meter) METER) Merers) MerTeERs) 
Num-| Per |Num-| Per |Num-| Per |Num-| Per |Num-| Per 
ber | Cent | ber | Cent | ber | Cent | ber | Cent | ber | Cent 
of of of of of of of of of of 
Plots | Plots | Plots | Plots | Plots | Plots | Plots | Plots | Plots | Plots 
Andropogon scoparius...... 57 | 89.1 | 64 |100.0] 16 |100.0 | 36 {100.0 9 | 100.0 
Solidago nemoralis......... AD G50 59s (592127 1G) 1000" 36510080 9 | 100.0 
Desmodium ciliare......... 2 Sell 8 U2) 6 | SHS.) 33° Sale 9) 10050 
Bouteloua curtipendula..... 3 ey 32.8 oes SS pO 9 | 100.0 
Lespedeza stipulacea........ 3 Ar | 2S) NW BSS | WA STO I I ekectt 9 | 100.0 
emeurdia satiimecri(?)......| 9 | 14.1 | 21 | 32.8) 13 | 81.3} 30. | 88.3 9 | 100.0 
Petalostemum purpureum. . . 3 ANT | ME PADIS NO) | E2GS. | BS» | OG 9 | 100.0 
Houstonia nigricans........ 3 ARH Al WS OSI yee) PO I) 0 9 | 100.0 
Lespedeza capitata......... 1 16 Ti LOES | SS | iss | SO. 7 77.8 
Euphorbia corollata......... 3 4.7 6 9.4 Sy SB) Uk | 60.6 5 55.6 
Funiperus virginiana....... — — 3 4.7 yg WP al Wen 0 aay ie) 6 66.7 
Senecio plattensis.......... oe — 1 1.6 1 6.3 Oe 2an0) ii 77.8 
Cassia fasciculata.......... — 3 4.7 PEW 2s) Fi 19.4 4 44.4 
Polygala verticillata........ 1.6 2 Srl Py NWS Ze elie tl 3 SES 
Panicum scribnerianum..... — = = zeae bal ea 3 SSE) 
Linum sulcatum........... — — 3 4.7 3 19.4 3 8.5 2 D2) 
ASSAULTS eae — — = = = = 3 5) 2 PED) 
Eragrostis spectabilis....... a — = = = = 2 5.6 ® YD) 
Andropogon gerardt........ = — = == — = 1 2.8 1 11.1 
EPEIGED SDs ces Sn ccs oi « — — — — = — 1 2.8 1 iki il 
IRUUSCOPGINUIE. . 0... sess = — 1 2.8 1 11.1 
Kuhnia eupatorioides....... — — — 1 2.8 1 Hilo 
Gerardia aspera(?)......... — = — 1 2.8 i ie 
MEE AIEM ISS. fel swcats tes 3), — 1 2.8 1 a 
Hedeoma hispida.......... = = = — = — 1 2.8 1 iliteal 
Ruellia humtlis..........:. — — = — — = 1 2.8 1 ed 
11 species 15 species 15 species 26 species 26 species 
64 plots 64 plots 16 plots 36 plots 9 plots 
