The Air -vesicles of Bladderworts. 211 



passing from rose-lilac to violet-blue, giving the cells the 

 aspect of painted glass, surrounded by silver threads. The 

 cells which closed the intercellular canals were either red or 

 dark blue, and surrounding them were other cells of reddish 

 tint. At the same pei-iod I found in the segments of the 

 leaves, by the side of green cells containing grains of chloro- 

 phyll, cells filled with a pale red fluid. The cells of the external 

 layer of the utricles contained chlorophyll grains, grouped 

 along their walls, whilst the interior was colourless. The cells 

 of mushroom form had their buttons always brown. 



The change of colour in the wall-cells of the utricles in 

 which we see the green pass into rose, lilac, violet, and blue, 

 depends evidently on a chemical action which has some rela- 

 tion to their contents and functions. It must be observed that 

 the colouration of the interior cells is due to a liquid, whilst the 

 granules of chlorophyll have disappeared, or did not exist. These 

 granules appear to have been exposed to a dissolving action, 

 and to an agency which has changed their colours. The red 

 colour of cellular liquids is usually ascribed to a free acid, and 

 the blue tint to the presence of an alkali. In the utricles of 

 the lesser Bladderwort all the transitions may be seen, from 

 bright red to dark blue. The cavity of the utricles contains at 

 the beginning a mucilaginous liquid of a neutral reaction, and 

 it is in this liquid that, at a later period, we see a little bubble 

 of gas, which gradually increases as the liquid diminishes. 

 We may easily satisfy ourselves of the presence of this liquid 

 by changing the position of the utricle, when the gas bubble 

 will be seen to reach the highest level by passing through a 

 viscous matter, which opposes a. certain resistance to its pas- 

 sage. In the month of June and July the vesicles are nearly 

 filled with air. The plant then rises to the surface of the 

 water, and the stalk which, in the lesser Bladderwort, bears 

 from two to five pale yellow flowers, stands up in the air, and 

 two unilocular anthers spread their pollen over the stigma of 

 the pistil, out of contact with the water. 



The ascensional force thus developed is very considerable. 

 Eeinsch* estimates the mean contents of a utricle as 2*57 

 cubic millimetres, and its weight as 0*0 milligrammes, and 

 the ascensional force of a single utricle will be equal to 1,964 

 milligrammes. There are about 597 utricles on a principal stem, 

 giving an ascending or floatation power of 0*778 grammes 

 for an entire plant. Beinsch reckons a total of 4*44 grammes. 

 (Beckoning four branches it would be 3' 11 2 grammes.) Now 

 the weight of the head of flowers which rise above the water 

 is 0'295 grammes; there is thus a considerable excess of 

 power capable of maintaining all the flowers above the water 



* " Mickroscop." 



