368 
soils of the United States, there should 
be no doubt concerning the ability of 
these soils to support such growth. In 
the Mediterranean region cork grows 
in both forest and steppe soils. Forest 
soil supports tree growth of practically 
all kinds, while steppe soil is too dry to 
support natural forest vegetation other 
than drought-resistant trees like the 
olive and the cork oak. If both forest 
and steppe soils support cork oak 
growth, it stands to reason that the 
chernozem and prairie soils, which 
are situated between them with respect 
to moisture, are satisfactory and may 
be considered potential soils. 
The soils in which the cork oak is 
growing vary widely in type ranging 
from the arid desert soils to the moist 
tropical soils. The range between the 
respective extremes is so great that it 
may safely be said that the cork oak 
shows no preference for any particular 
type of soil. However, it will not 
grow in marsh and swamp regions or 
in soils which are abundantly damp or 
poorly drained. 
The fact that the cork oak prefers 
no particular soil does not imply that 
the various types of soils are without 
effect on the rate of growth. A study 
of the effect of soils on the growth rate 
of cork, when temperature and rain- 
fall are constant, gave the following 
results: 
Soil region Rate of growth 
DD ESENtAis eaarnd rae eiteerae eee 0.95 
Steppe. 2s easement letters 1.00 
@hernozem ave aot incies gata sce 1.05 
Bra ire sc, popes cncpoes cost id edone! sptierenenenert 1.10 
ORESES so) sera diets ouelons eo useisneuetenees Tes) 
Gomplexcmeacie «sien eeesck 1.18 
Hl D) Ro) 0} (okt RI On tent int a acco 1.28 
Having completed the study of the 
independent effects of temperature, 
rainfall, and soil in relation to the dis- 
tribution and growth rate of the cork 
oak, further studies were made on the 
combined effect of these three climatic 
elements. Under varying conditions 
of temperature, rainfall, and soil the 
composite total rate of growth of cork 
will be the mathematical product of 
these three respective rates of growth. 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1948 
When a single composite, or cli- 
matic, environment is taken as a com- 
bination of one temperature region, 
one rainfall region, and one soil 
region, it is found that cork in the 
Mediterranean region is growing, un- 
der the 27 different environments 
listed in table 5, at rates between the 
limits of 0.58 and 1.45. 
TABLE 5.—Climatic environments of natural cork 
oak 
Compos- 
TemPer~) Rainfall Soil ite total 
a ae region region rate of 
8 growth 
50-55 10-20 | Steppe...... 0. 58 
50-55 10-20 | Tropical..... 1 
50-55 | 20-40 | Steppe...... 68 
50-55 20-40 | Forest....... 5 i 
50-55 20-40 | Complex.... . 80 
50-55 20-40 | Tropical..... Atsii/ 
50-55 | 40-60 |} Forest....... . 94 
50-55 | 40-60 | Complex.... OO 
55-60 10-20 | Steppe...... aia 
55-60 10-20 | Tropical..... . 90 
55-60 | 20-40 | Steppe...... 82 
55-60 | 20-40 | Forest....... 935 
55-60 20-40 | Complex.... ON 
55-60 | 20-40 | Tropical..... 1. 06 
55-60 40-60 | Steppe...... 1. 01 
55-60 | 40-60 | Forest....... 1.14 
55-60 | 40-60 | Complex 1. 20 
60-65 10-20 | Steppe...... . 86 
60-65 10-20 | Tropical..... 1.10 
60-65 | 20-40 | Steppe...... 1. 00 
60-65 | 20-40 | Forest....... 1.15 
60-65 | 20-40 | Complex... abs alte 
60-65 20-40 | Tropical..... 1. 28 
60-65 | 40-60 | Forest....... 17539 
60-65 | 40-60 | Complex 1. 45 
65-70 10-20 | Steppe...... 1. 04 
65=70 | Z0=40) erecta Osa ee t221 
A similar analysis of the United 
States potential cork area shows that 
it contains 38 different climatic en- 
vironments whose rates of growth lie 
between the limits of 0.55 and 2.31. 
From the data contained in tables 
2, 3, and 4, the composite total rate 
of growth for the Mediterranean 
region and each of its constituent 
countries was computed with the 
results shown in table 6. 
