LUMINOSITY OF PLANTS. 323 



668. Great differences of opinion have prevailed as to the existence 

 of a, proper heat in plants. Hunter examined the heat of the inter- 

 nal parts of the trunks of trees by boring holes of different depths in 

 them, and inserting thermometers; and similar experiments were made 

 by Schubler at Tubingen. The results of these experiments were, 

 1st. That the temperature of trees is higher than that of the air in 

 winter, and lower in summer ; 2d. That the temperature corresponds 

 to the depth in the soil to which the roots penetrate ; and, 3d. That 

 it depends on the temperature of the fluid matters taken up by the 

 roots, as well as the bad conducting power of the wood of the trees. 

 Dutrochet instituted a series of experiments to determine the tempera- 

 ture of the growing parts of plants. He found, by means of a thermo- 

 electric apparatus, that this varied from two or three-tenths of a 

 degree, to one degree above that of the air. This generation of heat 

 only takes place when the plant is active and vigorous, and seems to 

 be connected with processes going on in the interior of the cells. It 

 reaches a daily maximum, the period of which varies in different plants, 

 according to their vigour. Rameaux has confirmed Dutrochet's ob- 

 servations. There appear, therefore, to be two sources of heat in 

 plants, one depending on organic actions carried on in the growing 

 parts, and the other on meteorological influences, which either act 

 directly through the air, or indirectly through the fluid matters 

 brought up from a certain depth in the earth.* 



3. LUMINOSITY OF PLANTS. 



669. Luminous appearances have been observed in certain plants. 

 These have been long noticed in the lower classes of plants, such as 

 Fungi. Decaying wood, in which Fungi are developed, is sometimes 

 luminous. Mr. James Drummond describes some species of Agaric, 

 near the Swan River, growing on the trunks of Banksias and other 

 trees, which emitted at night a phosphorescent light sufficient to 

 enable him to read. A phosphorescent Agaric, with the upper sur- 

 face of the pileus black, while the centre and gills were white, was 

 noticed by him on the trunk of a dead Eucalyptus occidentalis. The 

 Agaricus Gardneri, found in Brazil, gives out a light of a pale greenish 

 hue, similar to that of fire-flies. It is found growing on a Palm, and 

 is called Flor de Coco. Delile found luminosity in the Agaricus 

 olearius, near Montpelier. In the coal mines of Dresden, certain 

 Rhizomorphous fungi have long been celebrated for the light which they 

 emit. The spawn of the Truffle (Tuber cibarium) is said to present 



* For further remarks on the Subject of Vegetable Heat, see Rameaux's papers in the Annales 

 <Tes Sciences Naturelles, January, 1843. Schubler's experiments in Poggendorff Annalcn, x. 092; 

 translated in Thomson's Chemistry of Vegetables, p. 959. Dutrochet, Ann. des Sc. Nat. (n. s.) 

 torn. xii. Gardner in Linn. Trans, for Dec. 1841, and in Philosoph. Mag. for July, 1812. 



