CHAPTER XI. 



OF THE PRODUCTION OF LIGHT, HEAT, AND ELECTRICITY BY 

 PLANTS. MOTIONS OF PLANTS. 



405. IT has been already stated that, by the operation of 

 these agents upon the Vegetable system, are chiefly maintained 

 those changes which make up the life of each being. (. 9.) If 

 Light be withdrawn, several of the most important of these are 

 speedily checked. If Heat be suspended, all of them directly 

 cease. With regard to the influence of Electricity, less is known, 

 and nothing can be positively stated. But Light, Heat, and 

 Electricity are not only required by Plants as conditions of their 

 growth ; but are sometimes produced by them. 



406. There are few instances in which Light is evolved from 

 Itving Plants ; but these few are very curious. Many flowers, 

 especially those of an orange colour, such as the Sun-flower, 

 Marigold, Nasturtium, Sec. have been said to disengage light in 

 serene and warm summer evenings, sometimes in the form of 

 sparks, sometimes with a steadier but more feeble glow. Light 

 is also emitted by certain species of Fungi, especially those which 

 grow in moist and warm places, where light is entirely excluded, 

 as in the depths of mines. The light is perceived in all parts of 

 the plant ; but chiefly in the young white shoots. It ceases if 

 the plant be deprived of oxygen, either by being placed in a 

 vessel from which the air has been exhausted, or in some other 

 gas ; and it re-appears, when the plant is restored to air. No 

 iuminousness is perceived after the death of the plant. It would 

 seem probable, therefore, that this extrication of light is in part 

 connected with that conversion of oxygen into carbonic acid, 

 which, as already mentioned, takes place very rapidly in flowers, 



