[Vor. 4 
206 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
plants will raise their temperature from 4 to 11° C. above 
that of the surrounding atmosphere. The effect of light as 
regards increase in temperature is therefore important. Still 
more significant is the influence of light on the course of cer- 
tain chemical reactions. Photosynthesis, for example, does 
not proceed in the absence of light. This, however, is an ex- 
tremely complex and incompletely understood example, and 
the following illustration may serve to make the point clearer. 
When two volumes of chlorine are mixed with one volume of 
methane and the mixture exposed to strong sunlight, a violent 
explosion occurs, resulting in the formation of hydrochloric 
acid and the deposition of carbon, i. е., CH, + 20 = С + 
4HCl. If the mixture is kept in the dark or diffuse light, 
chlorine substitution products are formed, i. e., CH4 + Cl; = 
CH3Cl-+ HCl, CHsCl+ Cl; = CHCl: + HCl, ete. This 
simple experiment serves to show the importance of light 
stimulus in the determination of the direction of certain 
chemical reactions. Since light plays such an important róle 
in the metabolic activities of green plants, its effect upon the 
manifestation of such a disturbance as the mosaic disease 
must be interpreted with the greatest reservation. 
TRANSMISSION OF THE Mosaic DISEASE THROUGH THE SEED 
A great deal of dissension may be noted in the literature 
on the transmissibility of the mosaic disease through seed. 
The early appearance of mosaic, which may occur in the 
second leaf, has led certain workers to conclude that the dis- 
ease must be carried over in the seed; yet, another sowing 
from the same sample of seed may yield plants which do not 
become diseased until they are half grown. Still greater con- 
fusion results when the idea is advanced that injury in trans- 
planting predisposes the plants to the malady. 
An attempt was made to throw further light upon this 
question, the method of growing plants in paper boxes as de- 
scribed above being adopted. About 1500 plants were handled 
in this manner. In some instances the tobacco seed was first 
sown in flats and then transplanted, while in other cases the 
