804 PHYSIOLOGY. 



of temperature. Probably this slight increase of heat under 

 such circumstances is due to the oxidation or combustion of a 

 portion of the carbon of the plant. Dutrochet found, however, 

 that when evaporation was allowed, 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 afternoon, the minimum 

 occurring at midnight. The variation, however, 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 in green and soft struc- 

 tures, 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 regard to the development 

 of heat by plants, and these are by no means of a satisfactory 

 nature. Much further investigation is required upon the deve- 

 lopment 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 authoi'ity 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 the so-called Rhizomorpha. According to Prescott, the my- 

 celium of the common Truffle is also luminous in the dark. 



The statement that certain Mosses, as ScJdstostega osmundacea 

 and Milium punctatmn, were phosphorescent, appears to have 

 been founded on imperfect observation. 



With regard to the development of light by the higher 

 classes of plants, we have at present no very satisfactory 

 observations 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, Eed 

 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 illusion, 

 and the fact of such luminosity having been only noticed in 

 flowers with such bright and gaudy tints, appears strongly to 

 favour such a conclusion. 



Tlie 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 Kuphorbia phcsphorea 

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



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



