The Air-vesicles of Bladderworts. 213 



to the surface. An air bubble, produced by a vegetative pro-. 

 ■cess, is detained amongst the petals, and in this bubble the 

 anthers deposit their pollen.* 



The evolution of gas in close cavities, which we see in a 

 certain number of aquatic plants, before the opening of their 

 flowers, is evidently connected with what is called vegetable 

 respiration. During this process, the plant not only takes 

 carbonic acid from the air or the water ; it absorbs oxygen at all 

 parts, which combines with certain vegetable matter, and 

 forms carbonic acid. The chemical action of solar light excites 

 the decomposition of the carbonic acid, which is absorbed, as 

 well as of that which the plant forms, the carbon being com- 

 bined with the elements of water and nitrogenous bodies, 

 while the oxygen is discharged. Stomata appears to play an. 

 important part in respiration, although, according to the re- 

 searches of Duchartre, there is no fixed relation between the 

 number and size of the stomata, and the quantity of gas which 

 the plants disengage under solar influence. 



In certain trees of a dry and coriaceous tissue, there is an 

 inverse relation between the number of stomata and the feeble- 

 ness of the gaseous evolution; but that which proves that 

 the gas evolved by the plant does not come from the stomata 

 only, is that we see it disengaged from the cells of the 

 epidermis of the upper surface of leaves of plants which have 

 no stomata in that position, when we plunge them under water. 

 We have noticed a similar evolution of gases from the sub- 

 merged leaves of Bladderworts. In aquatic plants which are 

 entirely submerged, the leaves have no stomata, and absorption 

 and exhalation take place from the whole surface of the 

 epiblema. The experiments of MM. Cloez and Gratiolet show 

 that the decomposition of carbonic acid by the green parts of 

 submerged plants only takes place under the influence of light. 

 In darkness, contrary to what takes place in aerial plants, no 

 carbonic acid is produced. A certain temperature is also 

 necessary for the process. It does not begin below 15° (0), 

 when the temperature is increasing, and cannot continue below 

 10°, when it is decreasing. The gas evolved by the plant 

 •contains a little nitrogen besides the oxygen. 



If we proceed to apply the preceding observations to the 

 leaves of the Bladderworts, we find them in water which is 

 usually very rich in carbonic acid, which is absorbed by the 

 leaves ; and, under the influence of light, oxygen, and a little 

 nitrogen are disengaged. These gases are also found in the 

 aeriferous canals which traverse the leaf segments, and they 

 escape from different points as small bubbles. We have seen 

 these bubbles escape through the walls of the utricles, which 

 * Ghi&in « Diet. d'Hist. IS T at." t. viii. p. 465. 



