346 PHYSIOGNOMY OP PLANTS. 



The Aroideae first led attention to the remarkable phenomenon of 

 the fever-heat, which in certain plants is sensible by the thermometer 

 during the development of their inflorescence, and which is con- 

 nected with a great and temporary increase of the absorption of 

 oxygen from the atmosphere. Lamarck remarked, in 1789, this 

 increase of temperature at the time of flowering in Arum italicum. 

 According to Hubert and Bory de St. Vincent, the vital heat of Arum 

 cordifolium in the Isle of France was found to rise to 35 and 39 

 Reaumur (110. 6 and 119. 6 Fahr.), while the temperature of the 

 surrounding air was only 15.2 R. (66.2 F.). Even in Europe, 

 Becquerel and Breschet found as much as 17 Reaumur difference 

 (39. 4 Fahr.). Dutrochet remarked a paroxysm, an alternate de- 

 crease and increase of vital heat, which appeared to reach a double 

 maximum in the day. Theodore de Saussure observed analogous 

 augmentations of temperature, though to a less amount, only from 

 0.5toO.8 of Reaumur's scale (1.15 to 1.8 Fahr.), in plants, 

 belonging to other families ; for example, in Bignonia radicans and 

 Cucurbita pepo. In the latter plant, the use of a very sensitive 

 thermoscope shows that the increase of temperature is greater in the 

 male than in the female plant. Dutrochet, who previous to his 

 early death made such meritorious researches in physics and in vege- 

 table physiology, found, by means of thermo-magnetic multiplicators 

 (Comptes rendus de Hnstitut, t. viii. 1839, p. 454, t. ix. pp. 614 

 and 781), an increase of vital heat from 0.l to 0.3 Reaumur 

 (0.25 to 0.67 Fahr.) in several young plants (Euphorbia lathyris, 

 Lilium candidum, Papaver somniferum), and even among funguses 

 in several species of Agaricus and Lycoperdon. This vital heat dis- 

 appeared at night, but was not prevented by placing the plants in 

 the dark during the day-time. 



A yet more striking physiognomic contrast than that of Casuari- 

 neae, Needle trees, and the almost leafless Peruvian Colletias, with 

 Aroideao, is presented by the comparison of those types of the 

 greatest contraction of the leafy organs with the Nymphaeaceae and 

 Nelumboneae. We find in these, as in the Aroideae, leaves, in which 

 the cellular tissue forming their surface is extended to an extreme 

 degree, supported on long, fleshy, succulent leaf-stalks ; as in Nym- 

 phaea alba ; N. lutea ; N. thermalis (once called N. lotus, from the 



