FUNCTIONS OF FLORAL ENVELOPES. 



259 



the cup of the flower, and sometimes in special pits or depressions, as 

 in Crown Imperial, and Asarabacca," attracts bees and various insects, 

 which are instrumental in disseminating the pollen. The quantity of 

 oxygen absorbed was determined by Saussure. He found that double 

 flowers absorbed less in proportion to their volume than single flowers ; 

 that the essential organs absorbed more oxygen than the floral enve- 

 lopes ; and that the greatest absorption took place when the stamens 

 and pistil were mature. 



The following are the results of some of Saussure's experiments : — 



While this oxidation is going on, carbon is given off in the form 

 of carbonic acid, and heat is evolved by the combination between the 

 oxygen and carbon. The quantity of carbonic acid evolved is in a 

 ratio corresponding to the amount of oxygen absorbed, and the degree 

 of heat present is proportionate to the activity of the chemical and 

 vital changes taking place. Experiments have been made as to the 

 amount of heat produced during flowering, especially by species of 

 Arum, Caladium, and Colocasia. These are plants in which the floral 

 envelopes are nearly absent, while the torus and growing point, and the 

 essential organs, attain a high degree of development, forming a spadix 

 enclosed in a large spathe. No heat eould be detected when the con- 

 tact of oxygen was prevented, either by putting the plants into other 

 gases, or by covering the surface of the spadix with oil. The surface 

 of the spadix is tha part whence the heat is chiefly evolved. Arum 

 cordifolium occasionally had a temperature 20° or 30° above that of 

 the surrounding air; Arum maculatum 17° to 20°; and Arum Dra- 

 cunculus and other species still higher. The following observations 

 were made by Brongniait on the spadix of Colocasia odora. The spathe 



