THE CHEMICAL ACTION OF LIGHT. 715 
enables the green plant to assimilate its food, and thus not only 
to make good the loss due to respiration, but to increase in weight. 
This is well illustrated by some experiments of Sachs, the 
results of which are shown in the following table. Four seeds of 
Tropeolum majus were sown in each of ten pots. When the 
seedlings appeared they were treated as follows :— 
1. Two pots were placed in a dark cupboard. 
2. Two pots were so placed in a room that they received 
only diffused daylight. 
3. Two pots were so placed in a window that they received 
diffuse daylight for seven hours daily. 
4. ‘Two pots were so placed in a window that they received 
diffuse daylight and often direct sunlight for about six hours daily. 
5. Two pots were so placed in a window that they received 
as much light, both diffuse daylight and direct sunlight, as possible. 
After twenty-five days the weights of the plants in the different 
pots were determined, with the following results :— 
Ie Ds 3- 4. i 
Gram. Gram. Gram. Gram. Gram. 
Weight of seeds....) 0°394 0°394 0°394 0°394 0°394 
»» 99 seedings 0°238 0°264 0°301 0° 480 I °292 
LISS gar earn o°156 0°130 0°093 — — 
SAIL Sis oYeccres aye ci — = — 0086 | 0'898 
/ 
Percentage loss ....| 39°6 33°0 23°6 — | — 
= gain....) — | = a 21'8 | 227°9 
It has already been said that it is by means. of the chlorophyll 
that green plants are able to avail themselves of the energy of the 
sun’s rays. Now, there are two opinions as to which rays of the 
spectrum are the most efficacious in promoting the decomposition 
of carbon dioxide by the chlorophyll, but the balance of evidence 
is in favour of the view that the rays which correspond to the 
