ACTINISM, LIGHT, AND HEAT. 371 



wood is formed, and upon their stimulus de- 

 pends the production of this refreshing green 

 which mantles over forest and field. But the 

 heat-rays are not less essential to the plant. 

 It appears that it is to the influence of the 

 heat-rays that we owe all those flower-beauties 

 in the vegetable world, which form such charm- 

 ing objects to the eye. It has been found that 

 by separating the heat-rays from light, by 

 means of a coloured glass, neither the light- 

 rays, nor the chemical rays, will enable the 

 plant to put forth flowers or fruit. For this 

 the heat-rays are essential, and, in some 

 wonderful and mysterious manner, by their 

 assistance, the plant becomes crowned with its 

 chiefest ornament. The influence of the che- 

 mical rays in germination has been already 

 noticed. 



We may thus recognise three stages in vege- 

 table life, in each of which one of the three 

 principles resident in the sunbeam comes most 

 prominently into operation. 1. In the in- 

 fancy of vegetable life, Actinism. 2. In the 

 youth of the plant, Light, properly so called. 

 And 3. In its perfection, or flowering-time, 

 Heat. It must not, however, be imagined that 

 at no other period in the life of the vegetable 

 being are these principles in active operation ; 

 this would be in the last degree erroneous. In 



