Jan., 1922] UPHOF — PLANTS IN SOUTHEASTERN MISSOURI 
3 
there is no snowfall. The average snowfall amounts to 275 mm. in the 
southeast, as compared with 600 mm. in the northwestern part of the state. 
The atmosphere is very humid and depressing. The rainfall in south- 
eastern Missouri is higher than that in any other part of the state. Al- 
though no exact data could be obtained, the following were derived from 
sources of the United States Weather Bureau: 800 to 950 mm. in parts of 
northern Missouri, 950 to 1,100 mm. in the middle section, 1,100 to 1,500 
mm. in the southeast being the mean annual rainfall over 21 years. During 
the summer rainless periods may occur of 2 to 6 weeks' duration; whereas 
sudden, heavy rainfalls accompanied by thunderstorms may occur at any 
time during the summer; these rains swell the rivers suddenly and cause 
them to overflow the surrounding country, especially the lowlands. 
The mean growing period of the vegetation lasts from March to October. 
Plant associations are very much diversified on account of their localities, 
such as small river valleys, ravines, barrens, mountain summits, rock out- 
crops, and small prairies; each one has its own plant societies. Frequently 
species are encountered belonging to southern states which are not to be 
found in the northern or middle part of the state. 
The forests of the Ozark hills are a predominant feature, being entirely 
different in composition from those of the lowlands. The soil of these 
hills is poor in organic matter as far as the slopes are concerned; the reddish- 
brown or grey soil, composed of very fine particles, is everywhere visible; 
when wet it is very sticky, when dry it is baked and very hard. Various 
oak species are here in the majority; although in a certain area one species 
of oak may be more frequently observed than in any other part of the hills. 
Toward the southern portion, e.g., in Butler County, Quercus marilandica 
Muench. forms a considerable part of the forest growth; in richer uplands 
Quercus imbricaria Michx. is often present; other species which are never 
absent are Q. stellata Wang. ; Q. falcata Michx. ; Q. macrocarpa Michx.; 
Q. alba L. ; Q. rubra L. ; hybrids of Q. alba X Q. macrocarpa and of Q. rubra 
X Q. falcata are also sometimes observed. The heaviest trees are always 
referable to Q. alba, Q. macrocarpa, and Q. rubra. 
Other genera of trees met with in such dry hills are, in the first place, 
several hickories, especially Carya glabra (Mill.) Spach, C. ovata (Mill.) 
K. Koch; where the soil is more fertile big trees of C. alba (L.) K. Koch 
also become common. Further, Diospyros virginiana L., Liquidambar 
Styraciflua L., Sassafras officinale Nees & Eberm., and Nyssa sylvatica 
Marsh, occur on such sterile soils; they become, however, far more common 
when the soil is fertile. Of smaller kinds of trees one notices especially in 
the spring before the leaves are unfolded the early flowering Cercis canadensis 
L., although it is as abundant in the rich bottom lands and ravines; at this 
time of the year the trees are covered with the beautiful pink-colored 
flowers; Cornus florida L. also grows in practically the same localities. On 
the other hand, Ulmus alata Michx., a species with conspicuously winged 
