374 
PHYSIOLOGY 
The best estimates as to the amount of photosynthesis carried on bv 
thin-leaved plants are given in the following table: 
CARBOHYDRATE MADE IN i HR. BY i SQ.M. OF LEAF SURFACE 
NAME OF PLANT 
CONDITION 
OP LEAF 
LIGHT 
TEMP. 
C. 
C0 t 
USED, 
CC. 
CO 2 
USED, 
MG. 
CARB. 
MADE, 
MG. 
i. Helianthus annuus . . 
attached 
diffuse 
21. 1 
312.6 
612 
39 2 
2. Helianthus annuus . . 
detached 
diffuse 
19.0 
439-9 
862 
551 
3. Helianthus annuus . . 
detached 
f strong to 
{diffuse 
26.8 
38S..3 
755 
483 
4. Helianthus annuus . . 
attached 
bright sun 
47.1 
21.9 
43 
27 
5. Tropaeolum majus . . 
detached 
diffuse 
21.7 
158.3 
310 
198 
6. Tropaeolum majus . . 
detached 
diffuse 
25-9 
243-7 
487 
305 
7. Catalpa bignonioides . 
detached 
interm. sun 
2O.O 
373-2 
737 
468 
8. Petasites albus . . . 
detached 
interm. sun 
17.0 
208.4 
408 
26l 
9. Polygonum Weyrichii . 
detached 
.... 
21.0 
473-2 
927 
593 
10. Prunus Laurocerasus . 
detached 
IO.O 
281 
ii. Prunus Laurocerasus . 
detached 
27. C 
810 
12. Helianthus annuus . 
detached 
J 1 O 
IO.O 
^60 
13. Helianthus annuus . 
detached 
20 o 
J^y 
6=;o 
14. Helianthus annuus . 
detached 
yw 
jir o 
V*J\^ 
7?o 
jj'^ 
/ o 
Nos. 1-9, after BROWN and ESCOMBE, in part recalculated ; nos. 10-14, after 
BLACKMAN and MATTHAEI, especially intended to show the effects of temperature 
on photosynthesis. An effect of excessive temperature is to be seen also in no. 4. 
Using such results as the basis of calculation, it would be easy to show 
how enormous a weight of food is made in a growing season by the foli- 
age of meadows and forests. But unknown allowances must be made for 
leaves unfavorably situated or lacking in vigor, and such estimates are 
of little value except for their impressiveness. The value and volume 
of the annual crops of cultivated plants is even more impressive; and 
to this must be added in imagination the unknown but huge volume cf 
wild vegetation, all dependent upon photosynthesis for at least 85 per cent 
of its dry substance. 
The following are the approximate values of some of the more important crops 
of 1909 in the United States: corn, $1,720,000,000; wheat, oats, rye, and barley, 
$1,280,000,000; cotton, $850,000,000; hay, $665,000,000; potatoes, $212,000,000. 
Together the weight of these marketable products is something like 175,000,000 
metric tons ; and of course this is but a small fraction of the vegetation that pro- 
