98 PLANT LIFE UF ALABAMA. 
The last killing frost happens between the middle of February and 
latter part of April, on the average, about the 8th or 10th of March. 
The maximum temperature was in July 106°; the minimum in Janu- 
uary 5°.1. The course of the temperature, which has such a potent 
influence on plant growth, is best represented in the following series 
of the absolute and average minima and maxima for each month dur- 
ing the same period: 
Series of maxt and mint temperatures. 
Jan. | Feb. | Mar.| Apr. | May | June] July | Aug. | Sept.| Oct. | Nov.| Dec, 
Maximum: 
Absolute 75.5 | 81.2 | 86.3 | 90 99 |105 106.9 |103 98 96.1 | 83 79 
Average 73.3 | 76.9 | 80.8 | 86.8 | 93.5 | 97.1 | 98.9 | 96 93 86.3 | 79 72.7 
Minimum: 
Absolute 4 14 25 30 44 48 60.8 | 59 31 21 
cae 
40 8 
24,5 | 33.2 | 40.5 | 50.7 | 61.1 | 69 65.5 | 52.7 | 40 29.1 | 22,8, 
me . 
XEROPHILE FORESTS. 
Post-oak prairies.—All over the region, particularly on the highest 
swells, the drifted clayey loams, sands, and pebbles mingle with the 
soil resulting from the decomposition of the underlying limestone 
strata, and give rise to light, more or less sandy, loams or heavy cal- 
careous clay soils, covered with open xerophile forests of Spanish oak, 
black oak, black jack, post oak, the last predominating, associated 
with mockernut and pignut hickory. Where the heavy clay soils 
prevail, destitute of humus, water-soaked during seasons of rain and 
baking to a hard crust during droughts, these so-called post oak prai- 
ries have been but little encroached upon. Under the cover of the 
brush the gramineous plant formations predominate, while sedge 
grasses (Cyperaceae) abound in the more shaded and wet situations. 
For example, Lleocharis tuberculosa, EF. ovata,’ and Cyperus pseudo- 
wegetus,” on the borders of ditches and pools; Carex triceps, a very 
distinct southern type, occurring from South Carolina to central 
Texas, but not in this State north of the southern edge of the meta- 
morphic hills; C. hirsuta,’ C. oblita, C. sterilis,’ C. lurida,* common 
throughout the Carolinian area; C. oxylepis, C. cherokeensis, C. debilis 
pubera of a more southern range; together with Panicum melicarium, 
P. anceps, and Uniola taxa. In drier and more exposed places: 
Scleria triglomerata’ (abundant). Steironema, ciliatum.! 
Allium canadense.1 Steironema lanceolatum.) 
Quamasia esculenta. Penstemon hirsutus.! 
Lobelia appendiculata. Hibiscus incanus. 
The last is a stately perennial of the Louisianian area known from 
a few localities between South Carolina and northwestern Louisiana. 
1See footnote }, p. 26. 
? Rarely found north of the Central Pine belt. 
