SECT. xiv. COLOURING MATTER. 429 



gen from the atmosphere, and exhale carbonic acid gas 

 exactly like animals. During the chemical combina- 

 tions of the oxygen with the carbon derived from the 

 nutriment to form the carbonic acid gas, heat is neces- 

 sarily evolved, especially in the flower, the point of 

 maximum heat varying widi its expansion. The blos- 

 soms of the Aroidese, or Arums, are remarkable for the 

 evolution of heat. According to Saussure, a blossom 

 of the common Arum maculatum consumes five times 

 its volume of oxygen in twenty-four hours previous to 

 its evolution of fruit, so it is not wonderful that the 

 chemical combination of such a quantity of oxygen 

 should produce a strong development of specific tempe- 

 rature. By M. Dutrochet's observations, the heat 

 evolved by the Arum maculatum has a maximum in the 

 day and a minimum in the night, and he found that it 

 exceeded the heat of the surrounding air by between 

 25 and 27. The heat of the Colocasia odorata, another 

 Arad, was determined by several observers to be even 

 50 above the warmth of the air. The heat evolved by 

 germinating seeds when in a heap is not from ferment- 

 ation ; it is owing to their consumption of oxygen and 

 expiration of carbonic acid gas. The temperature of all 

 vegetating parts of plants, the roots, leaves, young juicy 

 shoots, &c., is far superior to that of their flowers. It 

 arises from the nutritive process, and has a maximum 

 at noon, and a minimum at midnight, like that of the 

 flower. The growth of plants is most vigorous at noon ; 

 consequently there is then a greater evolution of heat. 



Water in small quantities is secreted night and morn- 

 ing from the points of the leaves of many plants, pro- 

 bably to relieve them from a superabundance of liquid, 

 which evaporation is insufiicient to carry off. The 

 arums are remarkable for the quantity they eject. It 

 falls in drops from the points of the leaves. About half 

 a pint is given out every night by the enormous leaves 

 of the Caladium distillatorium, a species of Arad. In 



