86 
such ecological factors as the amount of moisture and light, and 
to'the physical condition of the soil caused by the mat of hem- 
lock needles that accumulates beneath the trees. 
The following table gives the average growth per hour for 
each of the solutions 
7 Average Growth per Hour. 
Grams of Soil 
i | - H Sf] 
Date 1906. Se soe Seeding, Growth. aaa Hemlock Soil | Deciduous Soil 
P —: Extracts. Extracts, 
Aug. 28 | Sifted Corn 66 2 1.9901 mm. | I. ae mm. 
‘ “ “ “ 4 1.8674 9797 
“ “ “6 oe 8 I 9536 at 3 
“ “ “ ae 16 1.6565 1.3287 
July 2 - Lupine a: 2.5 0.7007 0.7045 
“ “ +6 Re 5 0.8030 | 0.9015 
“ “ te “ | 10 6666 8257 
“ “ “ “ | 20 0.7727 0.8143, 
Aug. 28 ae fs “ | 2 0.6098 0.5464 
ae ae ae oe 4 0.7121 0.5075 
= . . 8 0.5719 0.7575 
a a “ ‘fe 16 0.9500 0.7310 
"© 25 | Unsifted 7 “s 2.5 0.7803 0.6136 
ed in = 5 0.7592 9.7575 
« “ « “ to 7234 0.7811 
‘ “ “« “ 20 0 7766 0.7875 
Sept. 6 Sifted ff < 2.5 0.5075 0.4356 
e ce ce ce 5 ¥.4376 0. 5643 
6 “ “ce « 10 0.6969 0.6250 
“ ce “ “ 20 0.8068 0.6477 
July 21 Check oe ts Dist. water | 0.6477 
Aug. 25 ee “ce oe cad ae 0.4545 
Sept. 6 ec e “ee oe “ce 0.3863 
The results in the table are too obvious in their significance to 
call for discussion. 
Fernow (U.S. Dept. Agr. Div. For. Bul. 1891) says: 
“ ree to aa ceriiey to soil we need eoisider ae the physical 
condition of the soil, for forest trees require such small amounts 
of mineral matter that it is questionable whether a soil could be 
found that does not contain in sufficiency those that seem 
necessary.” 
According to Dr, Ebermeyer (Fernow, Garden and Forest 6: 
34. 1893) the air in the forest soil contains less carbonic acid 
than that of the field, varying from three to four times less in the 
