AGRICULTURAL TEXT-BOOK. 45 



tially different. Yellow light, (a,) impedes germination, and 

 accelerates that decomposition of carbonic acid, which produces 

 wood and woody tissues. Under its influence, leaves are small 

 and wood short jointed. Red light, (b,) carries heat, and is 

 favorable to germination if abundance of water is present, in 

 creases evaporation, supports the flowering quality, and improves 

 fruit. Under its influence, color is diminished, and leaves are 

 scorched. Blue light, (c,) (also called chemical action, or ac 

 tinism,) accelerates germination, and causes rapid growth. Under 

 its influence, plants become weak and long jointed. (Hunt.) 

 These three agencies exist in different proportions in the sun 

 beam in the spring, summer, and autumn. The blue, (c,) is 

 greater in spring; the yellow, (a,) in summer. The blue, 

 (chemical ray,) is less in the fall ; and then the heating ray, red, 

 (b,) predominates. Thus the sun s rays differ in their properties 

 at different seasons of year; and are adapted to the peculiar 

 needs of the plant at the time. Still further, the proportion of 

 these agencies vary in different latitudes and climates. Daguer 

 reotypes, depending on these principles, are poor in England, 

 better in France, superior in New York, but best in the North 

 western States. Probably the chemical rays are more abounding 

 in the above proportion, but there is yet much to learn on this 

 subject ; and it is not unlikely that the many differences known 

 to exist in animal and vegetable life in these countries will be 

 found to be more or less controlled by these peculiarities of the 

 sun s rays. Gardeners have attempted to make practical use of 

 these facts by means of colored glasses, but, apparently, without 

 much success. 



135. Rain is necessary for the life of most plants. In those 

 countries where rain never falls, vegetation is either wanting, or 

 depending on dews very limited. In other countries, where 

 it only falls at a certain season, leaving many months at a time 

 without a shower, plants only grow during the rains, and are 

 parched up and disappear during the rest of the year. The 



