OP THE ORGANS OF REPRODUCTION. 747 



component cells, and when in this state, as is commonly the 

 case with the bracts and the parts of the calyx, they perform 

 the same functions as ordinary leaves. When coloured, however, 

 as is generally the case with the corolla, and occasionally with the 

 bracts and calyx, they appear to have, in conjunction with the 

 receptacle or thalamus, a sj^ecial function to perform ; which 

 consists in the formation of a saccharine substance from the 

 amylaceous matter stored up in them. This saccharine matter is 

 designed more especially for the nourishment of the essential 

 organs of reproduction. That such is the function of these 

 parts seems to be proved hy the varying composition of the 

 thalamus at different periods of the flowering stage. Thus, at 

 the period of the opening of the flower, the thalamus is dry and 

 its cells are filled with amylaceous matters; as flowering pro- 

 ceeds, these matters become converted into saccharine substances, 

 upon which the surrounding parts are nourished ; and finally, 

 after floAvering it dries up. In fact, a similar change takes 

 place in the process of flowering in the composition of the con- 

 tents of the surrounding parts, as in the process of gemiination, 

 where the amylaceous matters are in like manner converted 

 into saccharine. 



When the saccharine matter is in excess during the process 

 of flowering, it is found upon the parts in a liquid state, and 

 may be removed without the flower suffering therefrom. 



In this conversion of amylaceous into saccharine matter, 

 oxygen is absorbed from the atmosphere, and carbonic acid gas 

 given off in a corresponding degree. Hence, the action of the 

 coloured parts of the flower or those not green, upon the sur- 

 rounding air, is directly the reverse of that of the green leaves 

 and other green organs whilst under the influence of solar light. 

 The absorption of oxygen thus noticed as occurring in the 

 coloured floral envelopes, also takes place in a still greater degree 

 in the essential organs of reproduction; hence, such an effect is 

 more evident in perfect flowers, than in those in which the 

 stamens and carpels have been more or less changed into petals 

 — that is, when the flowers have become partially or wholly 

 double. It has been proved also, that staminate flowers absorb 

 more oxygen than pistillate ones. 



The combination which under the above circumstances takes 

 place between the carbon of tlie flower and the oxygen of the air, is 

 attended by an evolution of heat, which indeed is always the 

 case where active chemical combination is going on. This 

 evolution of heat in the majority of flowers is not observable, 

 because it is immediately carried off" by the surrounding air; 

 but in those cases, where many flowers are crowded together, and 

 more especially when they are surrounded by a leafy stnicture, 

 such as a spathe, which confines the evolved heat, it may be 

 readily noticed. The flowers of the male cone of Cycas circi- 



