386 ILtiNnois NATURAL History SuRVEY BULLETIN Vol. 26, Art. 5 . 
Table 7.—Foliage area (square inches) for Table 8.—Foliage area (per cent of total — 
plants in the central milacre of Sampson and 
of Phegley hill prairies. 
Species OR TyPE OF SAMPSON | PHEGLEY 
PLant GrowTH PRAIRIE | PRAIRIE 
Andropogon scoparius...... 4,809 1,994 
Andropogon gerardi........ 27 0 
Bouteloua curtipendula..... 60 285 
All bunch grasses......... 4,896 2,279 
Plants other than grasses... 92 246 
All plants. 25 US os tipi 4,988 2.525 
In order to estimate foliage area of 4. 
scoparius in the central milacre of Samp- 
son, the writer multiplied the ground- 
space value of this grass by 2.7. The 
same factor was used in order to estimate 
foliage area for 4. gerardi. For Boute- 
loua curtipendula, a factor of 2.06 was 
used; this figure was indicated by separa- 
tion of the sample from Mud Creek prai- 
rie. The estimated foliage area for all 
grass species in the central milacre of 
Sampson was 4,896 square inches, table 
7. For Solidago rosettes, growing on the 
surface of the soil, foliage area was as- 
sumed to be the same as ground space. 
The lichens, Lecidea, are not included 
here as their thalli—simple plant bodies 
without true roots, stems, or leaves— 
grow under the foliage cover of other 
plants and thus do not contribute to fo- 
liage area. The estimated foliage area of 
Agave and Opuntia was 10.35 square 
inches. For the remaining 251 plants, 
mostly seedlings or small plants, the fo- 
liage area was estimated at 0.2 square 
inch per plant. The aggregate foliage 
area of plants other than grasses was es- 
timated to be 92 square inches. The total 
estimated foliage area in the central mil- 
acre of the Sampson prairie was 4,988 
square inches or 79.52 per cent of the 
milacre, tables 7 and 8. 
In the Phegley prairie, both in the cen- 
tral milacre and in the prairie as a whole, 
Andropogon scoparius showed obvious re- 
duction of cover, fig. 12, both at ground 
level and at foliage levels as compared 
with this species in the unpastured prai- 
rie. The leaves covered an area larger 
than the ground space, but not so large as 
the area covered by the leaves in the 
Sampson prairie. Foliage area for 4. sco- 
area) for plants in the central milacre of © 
Sampson and of Phegley hill prairies. 
SPECIES OR TYPE OF SAMPSON | PHEGLEY _ 
PLtanr GrowTH PrarriE | PRAIRIE 
Andropogon scoparius......| 76.66 31.79 
Andropogon gerardi........ 0.43 0.00 
Bouteloua curtipendula..... 0.96 4.54 
All bunch grasses..........| 78.05 36.33 
Plants other than grasses... 1.47 3.92 
All plants soi.) Si. Geeta 9.52 40.25 
parius in the central milacre of the Pheg- 
ley prairie was estimated at 1.8 times the 
ground space; this factor multiplied by 
the ground space gave an aggregate fol- 
iage area of 1,994 square inches, table 7. 
For Bouteloua curtipendula, the factor 
2.06 was again used (as in Sampson), 
which gave for this species in Phegley an 
estimated foliage area of 285 square 
inches. Plants of Lespedeza stipulacea, 
with an estimated foliage area of 1.5 
square inches per plant, had an estimated 
aggregate area of 106 square inches. For 
prostrate rosettes of Solidago, the foliage 
area was considered to be equivalent to 
ground space (as in Sampson). For the 
remaining plants, all small and mostly 
seedlings, foliage area was estimated at 
0.2 square inch per plant. Plants other 
than grasses had an estimated aggregate 
foliage area of 246 square inches. ‘The 
total estimated foliage area in the central 
milacre of the Phegley prairie was 2,525 
square inches, or 40.25 per cent of the 
milacre, tables 7 and 8. 
Available Space per Plant.—Avail- 
able space per plant, the inverse of plant 
density, is another character that, like 
density, can be useful in descriptions and 
comparisons of vegetation. It is simply 
obtained by dividing the area of the meas- 
ured sample by the number of plants in it. 
Variables affecting available space per 
plant are size of plants, degree of crowd- 
ing, and percentage of the measured area 
covered by plants. In those vegetations 
which show great disparity in sizes of 
plants of different species, as sagebrush 
with short-grass, average available space 
per plant should be separately found for 
each component or layer. In the Illinois 
hill prairies studied, individuals of the 
