390 
size in Sampson was more nearly ade- 
quate than the 1/256-milacre size in this 
unpastured prairie; + species of the 13 
found in the 64 plots of the 1/64-milacre 
size attained a percentage of 50 or more. 
These 4 species represented 30.77 per cent 
of the number of species found in the 64 
plots. 4. scoparius occurred in all the 
quadrats of the 1/64-milacre size. It is 
evident that the 1/16- and the 1/4-milacre 
plots (C and D in table 10) gave good 
ILtinois NATURAL History SurvEY BULLETIN 
Vol. 26, Art. 5 
Frequency Values for Combina- 
tions of Species.—In Sampson and 
Phegley prairies, certain species of plants 
occurred together in so many plots as to 
call attention to the combinations. In 
Sampson, the species in combination were 
Andropogon scoparius, Solidago nemoralis, 
Houstonia nigricans, and Desmodium cil- 
iare. In Phegley, they were Andropogon 
scoparius, Solidago nemoralis, Desmodium 
ciliare, and Bouteloua curtipendula. The 
Table 12.—Frequency of occurrence of characteristic combinations of plant species, Samp- 
son and Phegley hill prairies. 
Sampson ComMBINATION* 
PHEGLEY ComMBINATIONT 
NuMBER SI1zE 
nee Gaspar Number of Per Cent of Number of Per Cent of 
Occurrences Occurrence Occurrences Occurrence 
Pe 2 1 9 100.0 9 100.0 
36 1/4 31 79.5 30 83.3 
16 1/16 15 93.8 2 12:5 
64 1/64 19 29.7 1 se 
64 1/256 2 3.2 0 0.0 
* Combination in Sampson hill prairie: Andropogon scoparius, Solidago nemoralis, Houstonia nigricans, and Des- 
modium ciltare. 
7 Combination in Phegley hill prairie: Andropogon scoparius, Solidago nemoralis, Desmodium ciliare, and Boutcloua 
curtipendula. 
distribution among species. In the one 
(C), with a small number of plots and 13 
species, 7, or 53.85 per cent, attained a 
percentage of 50 or more; in the other 
(D), with a large number of plots and 
18 species, 7, or 38.88 per cent attained 
a percentage of 50 or more. In Sampson 
prairie, the frequency study showed, plots 
of 1/64 to 1/4 milacre were of sufficient 
size to give a satisfactory distribution of 
species. 
Phegley Prairie—Table 11 summa- 
rizes the data for the frequency study in 
pastured Phegley prairie. As in Sampson, 
the 1/256-milacre size was much too 
small to give good distribution; only 4n- 
dropogon scoparius attained a high fre- 
quency percentage. The 1/64-milacre 
size did not give good distribution of spe- 
cies; only two, 4. scoparius and Solidago 
nemoralis, attained percentages of 50 or 
more. These species represented 13.33 per 
cent of the total found in the 64 plots of 
this size. In Phegley prairie, the fre- 
quency study showed, plots of 1/16 to 
1/4 milacre were of sufficient size to give 
a satisfactory distribution of species. 
frequency values for these combinations 
of species are summarized in table 12. For 
the two larger plot sizes, 1/4 and 1 mil- 
acre, the sample was the 9-milacre square. 
For the 1/64- and 1/16-milacre sizes, 
the sample was the central milacre of the 
9-milacre square. For the 1/256-milacre 
size, the sample was 1/4 milacre, the 
northwest quarter of the central milacre. 
If the 1/4-milacre size had been studied 
in only the central milacres, the percent- 
age of occurrence of the characteristic 
combinations for ‘both Sampson and Pheg- 
ley would have been 100. 
Wherever one or more combinations of 
species can be discerned in any particular 
type of vegetation, the combinations can 
serve as a criterion of adequacy of plot 
size. In Phegley prairie, the 1/16-milacre 
size was obviously too small to give a 
fairly high frequency of occurrence for 
the characteristic combination; in Samp- 
son prairie, the 1/64-milacre size was too 
small. 
Frequency of occurrence of character- 
istic combinations of species has been used 
as a test of the adequacy of size of sam- 
