Vesicles of the Utricularix. . — 395 
0295 gramme ; consequently there is a very considerable excess 
of force; capable of maintaining the flowers out of the water 
through the whole time of fecundation. After this act, the 
utricles gradually beconie filled with liquid, the specific gravity 
of the plant increases, and it descends again slowly with its 
ripening fruits below the level of the water. The seeds, escaping 
from their unilocular capsule, fall into the mud, where they 
germinate*, 
We find among authors a difference of opinion as to the po- 
sition of the Utricularie in the water before flowering. Some 
regard them as attached to the bottom by slight roots; others 
(as, for example, Reinsch) regard them as floating plants. The 
Utricularie are really at first attached to the bottom; but 
the aériferous vesicles which are developed upon their leaves 
gently draw them out of the mud in which their filamentous 
roots bury themselves; and it is in this that I find the true 
utility of the utricles—namely, that they pull up the plant 
from the bottom; for the plant alone, without utricles, floats 
very well in the water, and rises towards the surfacet. 
The Uftricularie, however, are not the only plants in which 
we see such movements produced by an evolution of gas. In 
the Hottonie, Aldrovande, and Trapa natans we may discern, at 
the epoch of flowering, slow movements of displacement of the 
entire plant; whilst in other aquatic plants (Nymphea, Vallis- 
neria, Ranunculus aquatilis, &c.) only certain parts become elon- 
gated. In the Utricularie and Aldrovande it is by aériferous 
vesicles that the specific gravity of the plant is diminished and 
it is caused to rise by being drawn out of the soil. In the 
Hottonie we find, in the leaficts, cells filled with air. In the 
petioles of Trapa natans aériferous cavities are formed before 
the flowering (Reinsch, loc. cit.). 
Sometimes the plant cannot perfectly detach itself from the 
bottom ; the pollen-grains are then preserved in another man- 
hier from contact with the water. The following is a striking 
example, which shows us, as in the preceding cases, that at the 
approach of the flowering-seascn there is an evolution of gas, 
which, instead of producing a movement, plays a more direct 
part in fecundation. 7 
* The seeds are usually sterile; but there are large reproductive buds 
which descend to the bottom of the water during the winter (A. de Candolle, 
Géographie Botanique, tome ii. p. 1003). 
t I placed in a large glass vessel a tuft of Uiricularia furnished with 
vesicles which were still green; the plants floated at the surface of the 
water. Some Lymnee contained in the same vessel gnawed the plants, 
and especially devoured the utricles; the Utricularia, thus deprived of 
their vesicles, still maintained themselves at the surface. 
