788 PHYSIOLOGY. 



bustion of a portion of the carbon of the plant. Dutrochet 

 found, however, that when evaporation was allowed, that the 

 proper vital or specific heat of plants was slightly below that of 

 the atmosphere. He also noticed that the heat of plants varied 

 during the course of twenty-four hours, the hour of maximum 

 temperature varying from ten in the morning to three in the after- 

 noon, the minimum occurring at midnight. The variation, how- 

 ever, in such cases was extremely small in degree, being only from 

 about one-tenth to a little over one-half a degree of Fahrenheit. 

 This specific heat of plants could only be observed by him in 

 green and soft structures, those which were hard or woody not 

 possessing any specific heat. The above is but a brief summary 

 of the conclusions which have been at present arrived at with re- 

 gard to the development of heat by plants, and even these are by 

 no means of a satisfactory nature. Much further investigation 

 is required upon the development of heat by plants. 



2, Luminosity of Plants. — But very little is positively 

 known respecting the development of light by plants. It seems, 

 however, tolerably well ascertained, on the authority of Hum- 

 boldt, Nees von Esenbeck, Unger, Drummond, and others, 

 that the thalli of some living Fungi are luminous in the dark. 

 This luminosity has been noticed in several species of Agaricus 

 and Rhizomorpha. According to Prestoc, the myceHum of the 

 common Truffle is also luminous in the dark. 



The statement that certain Mosses, as Schistostega osmundacea 

 and Milium punctatum, were phosphorescent, appears to be 

 founded on imperfect observation. 



With regard to the development of light by the higher 

 classes of plants, we have at present no very satisfactory obser- 

 vations to depend upon. It has, however, been repeatedly 

 stated, that many orange and red-coloured flowers, such as 

 those of the Nasturtium, Sunflower, Marigolds, Orange Lilies, 

 Red Poppies, &c., give out, on the evening of a hot day in 

 summer, peculiar flashes of light. This peculiar luminosity of 

 orange and red flowers is now commonly regarded as an optical 

 delusion, and the fact of such luminosity having been only no- 

 ticed in flowers with such bright and gaudy tints, appears strongly 

 to favour such a conclusion. 



The rhizomes of certain Indian grasses have been reported to 

 be luminous in the dark during the rainy season ; and Mornay 

 and Martins have observed, that the milky juices of some plants 

 were luminous when exuding from wounds made in them. 

 Martins also states, that the milky juice of Euphorbia phosphorea 

 is luminous after removal from the plant, when it is heated. 



3. Electricity of Plants. — All the statements which have 

 been made upon the electrical condition of plants are vague 

 and unsatisfactory. It is said by some that electricity is deve- 

 loped during the ordinary growth of plants, as in germination 



