366 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1948 
TABLE 3.-——Rainfall distribution of natural cork oak 
Country 
Portugal: stsscycts4 cwistaties tae arte teats tebe ee 
S Pain ne shea cvsitvae ol cusler eet area hence eects 
Erance-and\Corsicassneeeoo ee eee le 
Italy,ySicily, and Sardinia’ wij 0.) a.)4- fi 
INSITE otdan euoomoNooe Onlg obtoIow Hoo biC 
French Morocco® voce cece nie treo 
Spanish Moroccolas. ws cele stoma er astetsirenel|(e 
Pumisia, Sts. ees teiteress + 2s Peseerae me reheat lier 
Percent in rainfall region of— 
Composite 
rainfall 
10’’-20"" | 20"-40’" | 40/7-60"" | (inches) 
Pigs) Ue) 4.6 27. 6 
39. 4 59. 6 1.0 24, 3 
sePoteegoes: 9559) 4,1 30. 8 
by), 2 37. 4 3. 4 21.8 
3. 4 SOFC sic cet 29.5 
56. 8 7 oe inl Lee Ree Aran HEE 
tbat eaters 100804). See 30. 0 
Blois Stra cic LOOMON seek Sees 30. 0 
24, 3 VERS) 22 26. 8 
to indicate healthy growth under less 
than 10 inches of annual rainfall. In 
the 60- to 80-inch regions cork is 
growing along the Pacific coast in 
northern California and along the 
Gulf coast in northwestern Florida. 
The cork trees in these localities are 
between 30 and 75 years of age, which 
is sufficient evidence that cork will 
grow between the Mediterranean 
maximum of 60 inches and the United 
States maximum of 80 inches of rain- 
fall. 
When the effect of rainfall on the 
rate of cork growth at constant tem- 
perature in the same soil was studied, 
the results were as follows: 
Mean annual 
rainfall (inches) Rate of growth 
LOPS aaicias aacetes Puetanc ne 0. 81 
7A Octane acaoterer rar CRIS CORR AVON 0 
SOK MPSS oe tey cates cuazcretere spehers 1. 00 
AU oraiy We BLA ME MY Des Oto Gla mem OIE Wo slat 
GQUe vps coro oaucee caro ene et ae 50 
Uae eGalcon at od valor tenon 1. 67 
Soil is the medium in which all 
plants grow, and its chemical com- 
position and physical structure de- 
pends upon the parent material from 
which it developed. The parent ma- 
terial, in turn, is largely character- 
istic of the underlying rock of which 
it was originally a constituent. There- 
fore, soils vary considerably in com- 
position, structure, and _ resultant 
fertility, depending upon both their 
lithic and climatic distribution. 
The soils of the world have been 
classified into nine primary groups 
called the zonal soils. Many similar 
soils, called intrazonal, are found in 
all climatic regions; and within the 
various zonal groups there may be 
found many different soils on the 
surface of the primary soil. These 
comparatively shallow surface soils are 
important for the growth of crops and 
grasses. In the case of trees, espe- 
cially the cork oak with its deep root 
system and exceptionally long tap 
root, it is felt that growth is a function 
of the soil substrata rather than the 
surface layers. For this reason, a 
study was made of the Mediterranean 
distribution of the cork oak in relation 
to the zonal soils and the result is 
presented in table 4, which shows that 
the cork oak is growing in the follow- 
ing primary soil groups, or regions: 
Brown steppe soils (or steppe). 
Gray-brown forest soils (or forest). 
Tropical and subtropical red and yellow 
soils (or tropical). 
Complex soils of mountains and included 
valleys (or complex). 
Table 4 also shows that the greatest 
amount (84.5 percent) of cork is grow- 
ing in the brown steppe soil region. 
These soils are usually in locations of 
decreased rainfall, or water supply, 
and are characterized as being semi- 
arid and highly calcareous. In some 
localities the lime is so concentrated 
