1156 
Journal of Agricultural Research 
Vol. XXVIII, No. II 
favorable than duff or litter to early germination of seed both from the stand¬ 
point of moisture and temperature conditions. 
Fortunately, during the period of seed germination,* the great extremes of sur¬ 
face soil temperature, which, if the soil were dry, would prove injurious to the 
tender seedlings, are effectively held in check by the high water content in soil 
and ash surfaces, for water has a very high specific heat of 1.0. 
INFLUENCE OF ASPECT 
Later in the summer, during July and August, the bare soil may become 
altogether too hot or too dry for the tender seedlings and cause death by* wilting 
A/ORTREAST 
SOUTHWEST 
ELAT 
A 
S 
A 
a 
A 
a 
A/ B 
A/ D 
A/ B 
A/ D 
N B 
A/ D 
90 
5 80 
6 60 
1 SO 
kj *0 
V 0 
_ 
t 
— 
\ 
\ 
v 
/ 
/ 
/ 
/ 
/ 
/ 
\ 
\ 
\ 
\ 
L/OHT 
SO/L TEMPERATURE 
MEA/V SO/L MO/STURE 
M/N/MUM SO/L 
MO/STURE 
t 
t 
I 
1 
\ 
N 
\ 
—v* 
\ 
/ 
/ 
/ 
\ 
% 
-r 
■'! 
i 
/ 
\ 
' 
v\ 
\ \ 
v \ 
\ \ 
\ \ 
-1_i 
/ / 
Ll 
V 
hA 
\ 
\ 
—V 
> 
/ 
»\ i 
/ \ 
\ 
— - 
_- 
Fig. 4.—Season average of soil temperatures, 1913. N, natural surfaces; B, burned surfaces, D, 
denuded surfaces 
/CO 
MAX/MUM 
M/N/MC/M 
90 
80 
<* 
, 70 
§ so 
30 
10 
iO 
— -- " 
AT* 
\\ 
- V'“ 
\ 
\ 
— 
SUREAt 
~E SO/L 
TEMPS. 
?ATOP£ 
S 
MAY JUNi f JULY AU6. SEPT OCT /VOX 
Fig. 5—Season average, 1913, beds A, C, and E 
or burning of the stems, or for want of sufficient soil moisture. It is from this 
standpoint that aspect and the degree of slope play an important part on seedling 
survival. The figures in Table VI merely summarize the high points of data 
obtained over a period of five years, from 1911 to 1916, on a northeast slope, a 
southwest slope, and a flat, all within one-half section of land. (See also fig. 4.) 
From the data in Table VI, and as shown in figure 5, it is seen that the absolute 
maximum surface temperatures and moisture content on the northerly slope 
never become critical for seedlings. But on the exposed flats and on southerly 
aspects the maximum surface temperatures have registered from 115° to 125° F., 
and the soil moisture has been as low as 3.4 to 0.5 per cent. These extremes 
ause death both by direct contact and by excessive evaporation, for on such 
